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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 20, 2017
Entity Information [Line Items]
Entity Registrant Name	REGENERON PHARMACEUTICALS INC
Entity Central Index Key	0000872589
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		105,528,158
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,911,456

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 792,065	$ 535,203
Marketable securities	586,879	503,481
Accounts receivable - trade, net	1,532,693	1,343,368
Accounts Receivable from Sanofi	217,478	92,989
Accounts receivable from Bayer	221,278	175,263
Inventories	641,588	399,356
Prepaid expenses and other current assets	143,761	130,528
Total current assets	4,135,742	3,180,188
Marketable securities	1,327,303	864,260
Property, Plant, and Equipment, Net	2,274,529	2,083,421
Deferred tax assets	927,023	825,303
Other assets	36,618	20,294
Total assets	8,701,215	6,973,466
Current liabilities:
Accounts payable and accrued expenses	818,426	879,096
Capital and facility lease obligations, current	0	129,557
Deferred revenue from Sanofi, current portion	187,036	115,267
Deferred Revenue, Current	132,832	116,397
Other current liabilities	334	1,178
Total current liabilities	1,138,628	1,241,495
Capital and facility lease obligations	702,317	351,569
Deferred revenue from Sanofi	408,786	503,474
Deferred Revenue, Noncurrent	274,666	327,298
Other long-term liabilities	125,225	100,385
Total liabilities	2,649,622	2,524,221
Stockholders' equity:
Preferred Stock	0	0
Additional paid-in capital	3,570,673	3,029,993
Retained earnings	2,773,214	1,748,222
Accumulated other comprehensive income (loss)	23,835	(12,840)
Treasury stock	(316,240)	(316,240)
Total stockholders' equity	6,051,593	4,449,245
Total liabilities and stockholders' equity	8,701,215	6,973,466
Class A Stock
Stockholders' equity:
Common stock	2	2
Common Stock
Stockholders' equity:
Common stock	$ 109	$ 108

CONSOLIDATED BALANCE SHEET (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	30,000,000	30,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Treasury Stock, shares outstanding (in shares)	3,763,868	3,763,868
Class A Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	40,000,000	40,000,000
Common Stock, shares issued (in shares)	1,911,456	1,911,456
Common Stock, shares outstanding (in shares)	1,911,456	1,911,456
Common Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	320,000,000	320,000,000
Common Stock, shares issued (in shares)	109,255,150	107,860,567

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Net product sales	$ 957,367	$ 857,468	$ 2,739,745	$ 2,475,869
Sanofi collaboration revenue	245,175	144,392	677,670	527,500
Bayer Collaboration Revenue	236,625	191,298	640,919	562,786
Other revenue	61,506	26,964	231,446	67,445
Total revenues	1,500,673	1,220,122	4,289,780	3,633,600
Expenses:
Research and development	529,749	543,047	1,547,159	1,573,089
Selling, general, and administrative	306,766	270,045	910,520	851,760
Cost of goods sold	46,388	29,901	149,774	150,090
Cost of collaboration and contract manufacturing	57,844	14,327	141,547	74,923
Total expenses	940,747	857,320	2,749,000	2,649,862
Income from operations	559,926	362,802	1,540,780	983,738
Other income (expense):
Other income, net	11,861	3,575	2,048	8,937
Interest expense, net	(6,182)	(496)	(19,084)	(4,387)
Total other income (expense)	5,679	3,079	(17,036)	4,550
Income before income taxes	565,605	365,881	1,523,744	988,288
Income tax expense	(177,288)	(101,077)	(498,752)	(345,881)
Net income	$ 388,317	$ 264,804	$ 1,024,992	$ 642,407
Net income per share - basic	$ 3.64	$ 2.53	$ 9.66	$ 6.14
Net income per share - diluted	$ 3.32	$ 2.27	$ 8.84	$ 5.51
Weighted average shares outstanding - basic	106,706	104,833	106,108	104,586
Weighted average shares outstanding - diluted	117,028	116,466	115,994	116,567
Statements of Comprehensive Income
Net income	$ 388,317	$ 264,804	$ 1,024,992	$ 642,407
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on marketable securities	21,485	(8,103)	36,645	(11,471)
Unrealized gain on cash flow hedges	2	0	30	0
Comprehensive income	$ 409,804	$ 256,701	$ 1,061,667	$ 630,936

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 1,024,992	$ 642,407
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	110,960	75,845
Non-cash compensation expense	380,144	405,320
Other non-cash charges and expenses, net	44,016	13,586
Deferred taxes	(108,242)	(190,327)
Changes in assets and liabilites
Increase in Sanofi, Bayer, and trade accounts receivable	(359,829)	(176,079)
Increase in Inventories	(235,645)	(99,706)
(Increase) decrease in prepaid expenses and other assets	(28,209)	34,857
(Decrease) increase in deferred revenue	(59,116)	282,176
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(28,908)	107,438
Total adjustments	(284,829)	453,110
Net cash provided by operating activities	740,163	1,095,517
Cash flows from investing activities:
Purchases of marketable securities	(883,748)	(606,153)
Sales or maturities of marketable securities	379,275	192,091
Capital expenditures	(164,963)	(361,486)
Net cash used in investing activities	(669,436)	(775,548)
Cash flows from financing activities:
Proceeds in connection with capital and facility lease obligations	57,000	5,085
Payments in connection with capital and facility lease obligations	(19,925)	(1,853)
Repayments of convertible senior notes	0	(12,650)
Payments in connection with deduction of outstanding warrants	0	(242,117)
Proceeds from issuance of Common Stock	226,892	89,777
Payments in connection with Common Stock tendered for employee tax obligations	(77,832)	(46,954)
Net cash provided by (used in) financing activities	186,135	(208,712)
Net increase in cash and cash equivalents	256,862	111,257
Cash and cash equivalents at beginning of period	535,203	809,102
Cash and cash equivalents at end of period	$ 792,065	$ 920,359

Interim Financial Statements (Notes)	9 Months Ended
Interim Financial Statements (Notes)	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interim Financial Statements	Interim Financial Statements The interim Condensed Consolidated Financial Statements of Regeneron Pharmaceuticals, Inc. and its subsidiaries ("Regeneron" or the "Company") have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all information and disclosures necessary for a presentation of the Company's financial position, results of operations, and cash flows in conformity with accounting principles generally accepted in the United States of America. In the opinion of management, these financial statements reflect all normal recurring adjustments and accruals necessary for a fair statement of the Company's financial position, results of operations, and cash flows for such periods. The results of operations for any interim period are not necessarily indicative of the results for the full year. The December 31, 2016 Condensed Consolidated Balance Sheet data were derived from audited financial statements, but do not include all disclosures required by accounting principles generally accepted in the United States of America. These financial statements should be read in conjunction with the financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016. Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.

Net Product Sales (Notes)

9 Months Ended

Sep. 30, 2017

Revenues [Abstract]

Product Sales and Concentration Risk [Text Block]

Product Sales



	Three Months Ended September 30,				Nine Months Ended September 30,
Net Product Sales in the United States	2017		2016		2017		2016
EYLEA^®	$	953,279	$	853,588	$	2,727,132	$	2,465,369
ARCALYST^®	4,088		3,880		12,613		10,500
Net Product Sales	$	957,367	$	857,468	$	2,739,745	$	2,475,869

The Company had product sales to certain customers that accounted for more than 10% of total gross product revenue for each of the three and nine months ended September 30, 2017 and 2016. Sales to each of these customers as a percentage of the Company's total gross product revenue are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Besse Medical, a subsidiary of AmerisourceBergen Corporation	51	%	54	%	51	%	56	%
McKesson Corporation	29	%	28	%	29	%	28	%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts	19	%	17	%	19	%	15	%

Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks, distribution-related fees, and other sales-related deductions. The following table summarizes the provisions and credits/payments for these sales-related deductions during the nine months ended September 30, 2017 and 2016.



	Rebates & Chargebacks			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2016	$	12,712		$	29,465		$	3,674		$	45,851
Provisions	121,599			140,860			33,518			295,977
Credits/payments	(108,811		)	(136,272		)	(21,444		)	(266,527		)
Balance as of September 30, 2017	$	25,500		$	34,053		$	15,748		$	75,301

Balance as of December 31, 2015	$	6,419		$	48,313		$	517		$	55,249
Provisions	63,510			113,755			22,812			200,077
Credits/payments	(62,503		)	(135,483		)	(19,587		)	(217,573		)
Balance as of September 30, 2016	$	7,426		$	26,585		$	3,742		$	37,753

Collaboration Agreements (Notes)

9 Months Ended

Sep. 30, 2017

Collaboration Agreement [Abstract]

Collaboration Agreements

a. Sanofi

The collaboration revenue the Company earned from Sanofi is detailed below:



	Three Months Ended September 30,						Nine Months Ended September 30,
Sanofi Collaboration Revenue	2017			2016			2017			2016
Antibody:
Reimbursement of Regeneron research and development expenses	$	128,539		$	131,389		$	421,056		$	469,223
Reimbursement of Regeneron commercialization-related expenses	90,339			64,418			251,002			213,957
Regeneron's share of losses in connection with commercialization of antibodies	(98,315		)	(112,001		)	(328,998		)	(333,530		)
Other	41,848			4,360			84,338			19,999
Total Antibody	162,411			88,166			427,398			369,649
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	61,649			36,226			188,408			97,851
Other	21,115			20,000			61,864			60,000
Total Immuno-oncology	82,764			56,226			250,272			157,851
	$	245,175		$	144,392		$	677,670		$	527,500

Antibodies

In November 2007, the Company entered into a global, strategic collaboration with Sanofi to discover, develop, and commercialize fully human monoclonal antibodies (the "Antibody Collaboration"). The Antibody Collaboration is governed by the companies' Discovery and Preclinical Development Agreement ("Antibody Discovery Agreement") and a License and Collaboration Agreement (each as amended). Pursuant to the Antibody Discovery Agreement, Sanofi agreed to fund up to $130.0 million of the Company's research activities in 2017. The Company's Antibody Discovery Agreement with Sanofi will end on December 31, 2017 without any extension and, therefore, funding from Sanofi under the Antibody Discovery Agreement will cease after 2017.

Under the License and Collaboration Agreement, agreed-upon worldwide development expenses incurred by both companies are funded by Sanofi, except that following receipt of the first positive Phase 3 trial results for a co-developed drug candidate, subsequent Phase 3 trial-related costs for that drug candidate ("Shared Phase 3 Trial Costs") are shared 80% by Sanofi and 20% by Regeneron. Consequently, during the three months ended September 30, 2017 and 2016, the Company recognized as research and development expense $22.6 million and $27.9 million, respectively, and during the nine months ended September 30, 2017 and 2016, the Company recognized as research and development expense $68.2 million and $80.2 million, respectively, of antibody development expenses that the Company was obligated to reimburse to Sanofi related to Praluent^®, Kevzara^® (sarilumab), and Dupixent^® (dupilumab).

"Reimbursement of Regeneron commercialization-related expenses" in the table above represents reimbursement of internal and external costs in connection with commercializing Praluent, Kevzara, and Dupixent. During the same periods that the Company recorded reimbursements from Sanofi related to the Company's commercialization expenses, the Company also recorded its share of losses in connection with the companies commercializing Praluent, Kevzara, and Dupixent within Sanofi collaboration revenue.

In March 2017, the U.S. Food and Drug Administration ("FDA") approved Dupixent for the treatment of adult patients with moderate-to-severe atopic dermatitis, and in September 2017, the European Commission granted marketing authorization for Dupixent for use in adults with moderate-to-severe atopic dermatitis who are candidates for systemic therapy. In May 2017, the FDA approved Kevzara for the treatment of adult patients with moderately to severely active rheumatoid arthritis, and in June 2017, the European Commission granted marketing authorization for Kevzara for the treatment of rheumatoid arthritis in adult patients.

Immuno-Oncology

In July 2015, the Company and Sanofi entered into a collaboration to discover, develop, and commercialize antibody-based cancer treatments in the field of immuno-oncology (the "IO Collaboration"). The IO Collaboration is governed by an Immuno-oncology Discovery and Development Agreement ("IO Discovery Agreement"), and an Immuno-oncology License and Collaboration Agreement ("IO License and Collaboration Agreement"). Pursuant to the IO Discovery Agreement, Sanofi will reimburse the Company for up to $200.0 million in 2017 to identify and validate potential immuno-oncology targets and develop therapeutic antibodies against such targets through clinical proof-of-concept. Under the terms of the IO License and Collaboration Agreement, the parties are co-developing the Company's antibody product candidate targeting the receptor known as programmed cell death protein 1, or PD-1 ("cemiplimab"). The parties share equally, on an ongoing basis, development expenses for cemiplimab.

The $640.0 million in aggregate up-front payments made by Sanofi during 2015 in connection with the execution of the IO Collaboration has been recorded by the Company as deferred revenue, and is being recognized ratably as revenue over the related performance period.

b. Bayer

The collaboration revenue the Company earned from Bayer is detailed below:



	Three Months Ended September 30,				Nine Months Ended September 30,
Bayer Collaboration Revenue	2017		2016		2017		2016
EYLEA:
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	205,367	$	170,854	$	571,126	$	484,181
Reimbursement of Regeneron EYLEA development expenses	6,053		2,219		10,833		7,186
Other	15,714		6,077		36,910		45,924
Total EYLEA	227,134		179,150		618,869		537,291
Ang2 antibody and PDGFR-beta antibody:
Reimbursement of development expenses	7,325		7,433		15,614		14,165
Other	2,166		4,715		6,436		11,330
Total Ang2 antibody and PDGFR-beta antibody	9,491		12,148		22,050		25,495
	$	236,625	$	191,298	$	640,919	$	562,786

EYLEA outside the United States

Under the terms of the license and collaboration agreement with Bayer for the global development and commercialization outside the United States of EYLEA, Bayer markets EYLEA outside the United States, where, for countries other than Japan, the companies share equally in profits and losses from sales of EYLEA. In Japan, the Company is entitled to receive a tiered percentage of between 33.5% and 40.0% of EYLEA net sales. In addition, the Company and Bayer share the funding of agreed-upon EYLEA development costs.

Ang2 antibody outside the United States

In March 2016, the Company entered into an agreement with Bayer governing the joint development and commercialization outside the United States of nesvacumab, an antibody product candidate to angiopoietin-2 (Ang2), including REGN910-3 (Ang2 in combination with aflibercept), for the treatment of ocular diseases or disorders. In connection with the agreement, Bayer made a $50.0 million non-refundable up-front payment to the Company and is obligated to pay 25% of global development costs and 50% of development costs exclusively for the territory outside the United States. The $50.0 million up-front payment was initially recorded as deferred revenue, and is being recognized ratably as revenue over the related performance period.

PDGFR-beta antibody outside the United States

In 2014, the Company entered into a license and collaboration agreement with Bayer governing the joint development and commercialization outside the United States of an antibody product candidate to Platelet Derived Growth Factor Receptor Beta (PDGFR-beta), including REGN2176-3, a combination product candidate comprised of an antibody to PDGFR-beta co-formulated with aflibercept. The agreement provided that the Company would conduct the initial development of the PDGFR-beta antibody through completion of the first proof-of-concept study, upon which Bayer would have a right to opt-in to license and collaborate on further development and commercialization outside the United States. Effective in the first quarter of 2017, the Company discontinued clinical development of REGN2176-3, and on July 31, 2017, the Company and Bayer agreed to terminate this collaboration agreement.

c. Mitsubishi Tanabe Pharma

In 2015, the Company and Mitsubishi Tanabe Pharma Corporation ("MTPC") entered into a collaboration agreement providing MTPC with development and commercial rights to fasinumab, the Company's nerve growth factor antibody in late-stage clinical development, in certain Asian countries. In connection with the agreement, MTPC made a $10.0 million non-refundable up-front payment, which was initially recorded as deferred revenue, and is being recognized ratably as revenue over the related performance period. In the first quarter of 2016, MTPC made additional payments totaling $60.0 million to the Company, which were recorded as deferred revenue and are being recognized ratably as revenue over the same performance period as the up-front payment.

In the second quarter of 2017, the Company earned, and recognized as a substantive milestone, a $30.0 million development milestone from MTPC upon initiation of a Phase 3 trial.

d. Teva

In September 2016, the Company and Teva entered into a collaboration agreement (the "Teva Collaboration Agreement") to develop and commercialize fasinumab globally, excluding certain Asian countries that are subject to the Company's collaboration agreement with MTPC (as described above). In connection with the Teva Collaboration Agreement, Teva made a $250.0 million non-refundable up-front payment in September 2016. The Company leads global development activities, and the parties share development costs equally on an ongoing basis. The $250.0 million up-front payment was initially recorded as deferred revenue, and is being recognized ratably as revenue over the related performance period.

The Company recognized revenue of $40.2 million and $141.0 million for the three and nine months ended September 30, 2017, respectively, and $5.2 million for the three months ended September 30, 2016, in connection with the Teva Collaboration Agreement. In the second quarter of 2017, the Company earned, and recognized as a substantive milestone, a $25.0 million development milestone from Teva upon initiation of a Phase 3 trial.

e. Intellia Therapeutics

In April 2016, the Company entered into a license and collaboration agreement with Intellia Therapeutics, Inc. to advance CRISPR/Cas gene-editing technology for in vivo therapeutic development. The Company collaborates with Intellia to conduct research for the discovery, development, and commercialization of new therapies, in addition to the research and technology development of the CRISPR/Cas platform. In connection with the execution of the agreement, the Company made a $75.0 million up-front payment, which was recorded as research and development expense in the second quarter of 2016. In May 2016, Intellia completed an initial public offering ("IPO") of its common stock; as part of the concurrent private placement, the Company purchased $50.0 million of Intellia common stock.

e. Adicet Bio

In July 2016, the Company entered into a license and collaboration agreement with Adicet Bio, Inc., a privately held company, to develop next-generation engineered immune-cell therapeutics with fully human chimeric antigen receptors ("CARs") and T-cell receptors ("TCRs") directed to disease-specific cell surface antigens in order to enable the precise engagement and killing of tumor cells. The Company collaborates with Adicet to identify and validate targets, and to develop a pipeline of engineered immune-cell therapeutics for selected targets. In connection with the execution of the agreement, the Company made a $25.0 million up-front payment to Adicet, which was recorded as research and development expense in the third quarter of 2016, and is obligated to provide Adicet with research funding over the course of a five-year research term.

Net Income Per Share (Notes)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Net Income Per Share

The Company's basic net income per share amounts have been computed by dividing net income by the weighted average number of shares of Common Stock and Class A Stock outstanding. Net income per share is presented on a combined basis, inclusive of Common Stock and Class A Stock outstanding, as each class of stock has equivalent economic rights. Diluted net income per share includes the potential dilutive effect of other securities as if such securities were converted or exercised during the period, when the effect is dilutive. The calculations of basic and diluted net income per share are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Net income - basic	$	388,317	$	264,804	$	1,024,992	$	642,407
Effect of dilutive securities:
Convertible senior notes - interest expense and amortization of discount and note issuance costs	—		—		—		397
Net income - diluted	$	388,317	$	264,804	$	1,024,992	$	642,804

(Shares in thousands)
Weighted average shares - basic	106,706		104,833		106,108		104,586
Effect of dilutive securities:
Stock options	9,809		10,156		9,386		10,340
Restricted stock	513		479		500		474
Convertible senior notes	—		—		—		81
Warrants	—		998		—		1,086
Dilutive potential shares	10,322		11,633		9,886		11,981
Weighted average shares - diluted	117,028		116,466		115,994		116,567

Net income per share - basic	$	3.64	$	2.53	$	9.66	$	6.14
Net income per share - diluted	$	3.32	$	2.27	$	8.84	$	5.51

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive include the following:



	Three Months Ended September 30,		Nine Months Ended September 30,
(Shares in thousands)	2017	2016	2017	2016
Stock options	4,515	7,687	8,892	7,842
Restricted stock	—	19	—	19
Convertible senior notes	—	3	—	—

Marketable Securities (Notes)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities as of September 30, 2017 and December 31, 2016 consist of both debt securities of investment grade issuers as well as equity securities.

The following tables summarize the Company's investments in marketable securities:



	Amortized		Unrealized					Fair
As of September 30, 2017	Cost Basis		Gains		Losses			Value
Corporate bonds	$	1,564,391	$	2,789	$	(2,691	)	$	1,564,489
U.S. government and government agency obligations	189,647		56		(645		)	189,058
Municipal bonds	4,614		—		(8		)	4,606
Commercial paper	61,464		—		—			61,464
Certificates of deposit	6,525		—		—			6,525
Equity securities	57,251		30,789		—			88,040
	$	1,883,892	$	33,634	$	(3,344	)	$	1,914,182

As of December 31, 2016
Corporate bonds	$	1,076,964	$	630	$	(4,743	)	$	1,072,851
U.S. government and government agency obligations	132,923		58		(641		)	132,340
Municipal bonds	7,663		1		(20		)	7,644
Commercial paper	63,074		1		—			63,075
Certificates of deposit	42,612		—		—			42,612
Equity securities	57,251		5,551		(13,583		)	49,219
	$	1,380,487	$	6,241	$	(18,987	)	$	1,367,741

The Company classifies its debt security investments based on their contractual maturity dates. The debt securities listed as of September 30, 2017 mature at various dates through September 2022. The fair values of debt security investments by contractual maturity consist of the following:



	September 30, 2017		December 31, 2016
Maturities within one year	$	586,879	$	503,481
Maturities after one year through five years	1,239,263		815,041
	$	1,826,142	$	1,318,522

The following table shows the fair value of the Company's marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position.



	Less than 12 Months					12 Months or Greater					Total
As of September 30, 2017	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	675,374	$	(2,111	)	$	110,545	$	(580	)	$	785,919	$	(2,691	)
U.S. government and government agency obligations	141,393		(591		)	6,943		(54		)	148,336		(645		)
Municipal bonds	4,105		(8		)	—		—			4,105		(8		)
	$	820,872	$	(2,710	)	$	117,488	$	(634	)	$	938,360	$	(3,344	)

As of December 31, 2016
Corporate bonds	$	759,222	$	(4,685	)	$	36,407	$	(58	)	$	795,629	$	(4,743	)
U.S. government and government agency obligations	81,170		(641		)	—		—			81,170		(641		)
Municipal bonds	7,141		(20		)	—		—			7,141		(20		)
Equity securities	36,417		(13,583		)	—		—			36,417		(13,583		)
	$	883,950	$	(18,929	)	$	36,407	$	(58	)	$	920,357	$	(18,987	)

There were no realized losses on sales of marketable securities, and realized gains were not material, for the three and nine months ended September 30, 2017. Realized gains and losses on sales of marketable securities were not material for the three and nine months ended September 30, 2016.

As it relates to marketable securities, for the three and nine months ended September 30, 2017 and 2016, amounts reclassified from accumulated other comprehensive income (loss) into other (expense) income, net were related to realized gains and losses on sales.

Fair Value Measurements (Notes)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company's assets that are measured at fair value on a recurring basis consist of the following:



			Fair Value Measurements at Reporting Date Using
As of September 30, 2017	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Corporate bonds	$	1,564,489	—		$	1,564,489
U.S. government and government agency obligations	189,058		—		189,058
Municipal bonds	4,606		—		4,606
Commercial paper	61,464		—		61,464
Certificates of deposit	6,525		—		6,525
Equity securities	88,040		$	88,040	—
	$	1,914,182	$	88,040	$	1,826,142

As of December 31, 2016
Available-for-sale marketable securities:
Corporate bonds	$	1,072,851	—		$	1,072,851
U.S. government and government agency obligations	132,340		—		132,340
Municipal bonds	7,644		—		7,644
Commercial paper	63,075		—		63,075
Certificates of deposit	42,612		—		42,612
Equity securities	49,219		$	49,219	—
	$	1,367,741	$	49,219	$	1,318,522

Marketable securities included in Level 2 are valued using quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model-based valuations in which significant inputs used are observable. The Company considers market liquidity in determining the fair value for these securities. The Company did not record any charges for other-than-temporary impairment of its Level 2 marketable securities during the three and nine months ended September 30, 2017 and 2016.

There were no purchases, sales, or maturities of Level 3 marketable securities and no unrealized gains or losses related to Level 3 marketable securities for the three and nine months ended September 30, 2017 and 2016. There were no transfers of marketable securities between Levels 1, 2, or 3 classifications during the nine months ended September 30, 2017 and 2016.

The fair value of interest rate swap and interest rate cap contracts, which were recorded within other assets (non-current) and other long-term liabilities, was not material as of September 30, 2017 (see Note 11). The fair value of these contracts was determined based on Level 2 inputs, using significant inputs that are observable either directly or indirectly, including London Interbank Offered Rate ("LIBOR") and interest rate swap rates.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Inventory (Notes)

9 Months Ended

Sep. 30, 2017

Inventory Disclosure [Abstract]

Inventory

Inventories

Inventories consist of the following:



	September 30,		December 31,
	2017		2016
Raw materials	$	187,029	$	92,287
Work-in-process	217,448		202,301
Finished goods	23,958		13,334
Deferred costs	213,153		91,434
	$	641,588	$	399,356

Deferred costs represent the costs of product manufactured and shipped to the Company's collaborators for which recognition of revenue has been deferred.

Accounts Payable and Accrued Expenses (Notes)

9 Months Ended

Sep. 30, 2017

Payables and Accruals [Abstract]

Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses consist of the following:



	September 30,		December 31,
	2017		2016
Accounts payable	$	153,946	$	134,984
Accrued payroll and related costs	166,102		153,086
Accrued clinical trial expenses	119,608		91,753
Accrued sales-related charges, deductions, and royalties	167,467		159,985
Income taxes payable	126,612		235,776
Other accrued expenses and liabilities	84,691		103,512
	$	818,426	$	879,096

Debt (Notes)	9 Months Ended
Debt (Notes)	Sep. 30, 2017
Debt Disclosure [Abstract]
Debt Disclosure [Text Block]	Debt a. Convertible Debt In the first nine months of 2016, the Company settled conversion obligations for $12.7 million principal amount of the Company's convertible senior notes (the "Notes") that was previously surrendered for conversion. Consequently, in the first nine months of 2016, the Company paid $12.7 million in cash and issued 118,822 shares of Common Stock. In addition, the Company allocated $47.1 million of the settlement consideration provided to the Note holders to the reacquisition of the equity component of the Notes, and recognized such amount as a reduction of stockholders' equity. The loss on the debt extinguishment in connection with the Notes that were surrendered for conversion during the first nine months of 2016 was not material. As a result of these Note conversions, in the first nine months of 2016, the Company also exercised a proportionate amount of its convertible note hedges, for which the Company received 118,808 shares of Common Stock, which was approximately equal to the number of shares the Company was required to issue to settle the non-cash portion of the related Note conversions. The Company recorded the cost of the shares received, or $10.0 million, as Treasury Stock during the first nine months of 2016. Warrant Transactions In November 2015, the Company entered into an amendment agreement with a warrant holder whereby the parties agreed to reduce a portion of the number of warrants held by the warrant holder. The reduction in the number of warrants was determined based on the number of warrants with respect to which the warrant holder closed out its hedge position, provided that the warrant holder did not effect any purchases at a price per share exceeding $535.00 per share, during the period starting on November 16, 2015 and ending no later than February 9, 2016. The Company was able to settle, at its option, any payments due under the amendment agreement in cash or by delivering shares of Common Stock. As a result of the warrant holder closing out a portion of its hedge position in the first quarter of 2016, the Company paid a total of $135.2 million to reduce the number of warrants held by such warrant holder by 360,406. In February 2016, the Company entered into an amendment agreement with a warrant holder whereby the parties agreed to reduce a portion of the number of warrants held by the warrant holder. The reduction in the number of warrants was determined based on the number of warrants with respect to which the warrant holder closed out its hedge position, provided that the warrant holder did not effect any purchases at a price per share exceeding $375.00 per share, during the period starting on February 22, 2016 and ending no later than May 5, 2016. The Company was able to settle, at its option, any payments due under the amendment agreement in cash or by delivering shares of Common Stock. As a result of the warrant holder closing out a portion of its hedge position during the first nine months of 2016, the Company paid a total of $106.9 million to reduce the number of warrants held by such warrant holder by 403,665. b. Credit Facility In 2015, the Company entered into an agreement with a syndicate of lenders which provides for a $750.0 million senior unsecured five-year revolving credit facility. As of September 30, 2017, the Company had no borrowings outstanding under the credit facility and was in compliance with all credit facility covenants.

Leases (Notes)	9 Months Ended
Leases (Notes)	Sep. 30, 2017
Leases disclosure [Abstract]
Leases of Lessee Disclosure [Text Block]	Leases The Company leases laboratory and office facilities in Tarrytown, New York (the "Tarrytown Leases"). Prior to December 30, 2016, certain of the premises under the Tarrytown Leases had been accounted for as operating leases, while for certain other buildings the Company leased, the Company was deemed, in substance, to be the owner of the landlord's buildings (collectively, the "Build-to-Suit Buildings") in accordance with the application of FASB authoritative guidance. On December 30, 2016, the Company entered into a Purchase Agreement with BMR-Landmark at Eastview LLC and BMR-Landmark at Eastview IV LLC (collectively, "BMR"), pursuant to which the Company agreed to purchase BMR's Tarrytown, New York facilities (the "Facility") for a purchase price of $720.0 million. The Company occupies a significant portion of the Facility, with the remaining rentable area under leases to third-party tenants. In accordance with the terms of the Purchase Agreement, the Company paid $57.0 million toward the purchase price to BMR in December 2016. Upon entering into the December 30, 2016 Purchase Agreement with BMR, the premises under the Company's Tarrytown Leases that were historically accounted for as operating leases were deemed to be modified, as the Company now had the option to purchase the Facility under terms that made it reasonably assured to be exercised. Consequently, the leases for such premises were re-classified as a capital lease upon execution of the Purchase Agreement, and a proportionate amount of the $57.0 million payment was recorded as reduction of the initial capital lease liability. The execution of the Purchase Agreement did not impact the balance sheet classification for the Build-to-Suit Buildings; however, a proportionate amount of the $57.0 million payment was recorded as a reduction to the related facility lease obligation. On March 3, 2017, the Company entered into a Participation Agreement with Banc of America Leasing & Capital LLC ("BAL"), as lessor, and a syndicate of lenders (collectively, the "Participants"). The Participation Agreement provided for lease financing in connection with the acquisition by BAL of the Facility and the Company's lease of the Facility from BAL. On March 3, 2017, the right to take title to the Facility under the Purchase Agreement was assigned by the Company to BAL, and the Participants advanced $720.0 million, which was used by BAL to finance the purchase price for the Facility and to reimburse the Company for the $57.0 million payment made to BMR in December 2016. The $57.0 million reimbursement was recorded by the Company in March 2017 as an increase to capital and facility lease obligations in amounts equal to those initially recorded upon making such payment to BMR in December 2016. On March 3, 2017, the Company entered into a lease agreement (the "Lease") with BAL, pursuant to which the Company has leased the Facility from BAL for a five-year term. As a result of entering into the lease agreement, certain parts of the Facility became subleased from the Company by existing third-party tenants. The Lease requires the Company to pay all maintenance, insurance, taxes, and other costs arising out of the use of the Facility. The Company is also required to make monthly payments of basic rent during the term of the Lease in an amount equal to a variable rate per annum based on the one-month LIBOR, plus an applicable margin that varies with the Company’s debt rating and total leverage ratio. The Participation Agreement and the Lease include an option for the Company to elect to extend the maturity date of the Participation Agreement and the term of the Lease for an additional five-year period, subject to the consent of all the Participants and certain other conditions. The Company also has the option prior to the end of the term of the Lease to (a) purchase the Facility by paying an amount equal to the outstanding principal amount of the Participants' advances under the Participation Agreement, all accrued and unpaid interest and yield thereon, and all other outstanding amounts under the Participation Agreement, the Lease, and certain related documents or (b) sell the Facility to a third party on behalf of BAL. The advances under the Participation Agreement mature, and all amounts outstanding thereunder will become due and payable in full at the end of the term of the Lease. As a result of entering into the lease agreement with BAL, the premises that were classified as a capital lease as of December 31, 2016 were reassessed. As described above, the Company has the option to purchase the Facility, and as a result, the Company is deemed to have continuing involvement in such premises. Accordingly, these premises continue to be classified as a capital lease, with the related property, plant, and equipment and capital lease liability remaining on the Company's Condensed Consolidated Balance Sheet. In addition, as described above, upon entering into the lease agreement, the Company began to lease space occupied by third-party tenants. The lease of such premises is also classified as a capital lease. The execution of the March 2017 lease agreement did not impact the balance sheet classification for the Build-to-Suit Buildings. However, during the first nine months of 2017, the Company recorded a $30.1 million loss on extinguishment of debt associated with the Build-to-Suit Buildings, and a corresponding decrease to property, plant and equipment. In the aggregate, the Company recorded $720.0 million of capital and facility lease obligations upon execution of the lease agreement for the Facility. The Participation Agreement and the Lease contain financial and operating covenants, which are substantially similar to the covenants set forth in the Company's credit facility (see Note 9). The Company was in compliance with all covenants of the Participation Agreement and the Lease as of September 30, 2017.

Derivative Instruments (Notes)

9 Months Ended

Sep. 30, 2017

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments and Hedging Activities Disclosure [Text Block]

Derivative Instruments and Hedging Activities

The Company is exposed to market fluctuations in interest rates, including those in connection with its March 2017 lease agreement (see Note 10). During the three and nine months ended September 30, 2017, the Company entered into interest rate swap and interest rate cap agreements to manage a portion of such interest rate risk. All of the Company’s derivative instruments are utilized for risk management purposes, and are not used for trading or speculative purposes.

The Company's derivative instruments are designated as cash flow hedges for accounting purposes. Since the specific terms of the derivative instruments match those of the item being hedged, the derivative instruments are deemed to be highly effective in offsetting the changes in cash flows of the hedged item. As such, changes in the fair value of these derivatives are recorded in accumulated other comprehensive income (loss) until the underlying transaction affects earnings, and are then reclassified to earnings in the same account as the hedged transaction. The Company would record any gain or loss related to the ineffectiveness directly to earnings.

The Company assesses, both at inception and on an ongoing basis, whether derivatives used continue to be highly effective in offsetting changes in cash flows of the hedged items. The Company does not exclude any portion of the cash flow hedge contracts from the assessment of hedge effectiveness. If and when a derivative is no longer expected to be highly effective, hedge accounting is discontinued.

The following table summarizes the notional amounts of the Company's outstanding interest rate swap and cap agreements as of September 30, 2017:



	Notional Amount
Interest rate swap contracts	$	75,000
Interest rate cap contracts	$	75,000

As it relates to cash flow hedges, for the three and nine months ended September 30, 2017, amounts of gains and losses recognized in other comprehensive income (loss), and amounts reclassified from accumulated other comprehensive income (loss) into interest expense, net, were not material. As of September 30, 2017, the amounts expected to be reclassified out of accumulated other comprehensive income into interest expense over the next 12 months is not expected to be material. For the three and nine months ended September 30, 2017, there were no gains or losses recorded related to the ineffective portion of the derivative instruments.

Income Taxes (Notes)	9 Months Ended
Income Taxes (Notes)	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company is subject to U.S. federal, state, and foreign income taxes. The Company recorded an income tax provision in its Statement of Operations of $177.3 million and $101.1 million for the three months ended September 30, 2017 and 2016, respectively, and $498.8 million and $345.9 million for the nine months ended September 30, 2017 and 2016, respectively. The Company's effective tax rate was 31.3% and 27.6% for the three months ended September 30, 2017 and 2016, respectively, and 32.7% and 35.0% for the nine months ended September 30, 2017 and 2016, respectively. The Company's effective tax rate for the three and nine months ended September 30, 2017 and 2016 was positively impacted, compared to the U.S. federal statutory rate, by the tax benefit associated with stock-based compensation, the domestic manufacturing deduction, and the federal tax credit for research activities, offset by the negative impact of losses incurred in foreign jurisdictions with rates lower than the U.S. federal statutory rate and the non-tax deductible Branded Prescription Drug Fee. The Company's effective tax rate for the three months ended September 30, 2016 was also positively impacted by changes to tax reserves. The Company also recorded an income tax provision of $6.4 million and $6.5 million in its Statement of Comprehensive Income for the three and nine months ended September 30, 2017, respectively, primarily related to unrealized gains on available-for-sale marketable securities. The Company recorded an income tax benefit of $3.3 million in its Statement of Comprehensive Income for the nine months ended September 30, 2016 primarily related to unrealized losses on available-for-sale marketable securities; such amount for the three months ended September 30, 2016 was not material.

Statement of Cash Flows (Notes)	9 Months Ended
Statement of Cash Flows (Notes)	Sep. 30, 2017
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Statement of Cash Flows	Statement of Cash Flows Supplemental disclosure of non-cash investing and financing activities Included in accounts payable and accrued expenses as of September 30, 2017 and December 31, 2016 were $24.5 million and $28.2 million, respectively, of accrued capital expenditures. Included in accounts payable and accrued expenses as of September 30, 2016 and December 31, 2015 were $33.9 million and $50.7 million, respectively, of accrued capital expenditures. The Company recognized an additional capital lease obligation of $201.2 million in connection with the Company's lease of additional premises at its Tarrytown, New York facility during the nine months ended September 30, 2017 (see Note 10). No such amount was recognized during the nine months ended September 30, 2016.

Legal Matters (Notes)	9 Months Ended
Legal Matters (Notes)	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Legal Matters	Legal Matters From time to time, the Company is a party to legal proceedings in the course of the Company's business. Costs associated with the Company's involvement in legal proceedings are expensed as incurred. The outcome of any such proceedings, regardless of the merits, is inherently uncertain. If the Company were unable to prevail in any such proceedings, its consolidated financial position, results of operations, and future cash flows may be materially impacted. Proceedings Relating to '287 Patent, '163 Patent, and '018 Patent The Company is a party to patent infringement litigation initiated by the Company involving its European Patent No. 1,360,287 (the "'287 Patent"), its European Patent No. 2,264,163 (the "'163 Patent"), and its U.S. Patent No. 8,502,018 (the "'018 Patent"). Each of these patents concerns genetically engineered mice capable of producing chimeric antibodies that are part human and part mouse. Chimeric antibody sequences can be used to produce high-affinity fully human monoclonal antibodies. In these proceedings, the Company claims infringement of several claims of the '287 Patent, the '163 Patent, and the '018 Patent (as applicable), and seeks, among other types of relief, an injunction and an account of profits in connection with the defendants' infringing acts, which may include, among other things, the making, use, keeping, sale, or offer for sale of genetically engineered mice (or certain cells from which they are derived) that infringe one or more claims of the '287 Patent, the '163 Patent, and the '018 Patent (as applicable). At this time, the Company is not able to predict the outcome of, or estimate possible gain or a range of possible loss, if any, related to, these proceedings. Proceedings Relating to Praluent (alirocumab) Injection As described in greater detail below, the Company is currently a party to patent infringement actions initiated by Amgen Inc. against the Company and Sanofi (and/or the Company's and Sanofi's respective affiliated entities) in a number of jurisdictions relating to Praluent, which the Company is jointly developing and commercializing with Sanofi. In the United States, Amgen has asserted a number of U.S. patents, which were subsequently narrowed to U.S. Patent Nos. 8,829,165 (the "'165 Patent") and 8,859,741 (the "'741 Patent"), and seeks a permanent injunction to prevent the Company and the Sanofi defendants from commercial manufacturing, using, offering to sell, or selling within the United States (as well as importing into the United States) (collectively, "Commercializing") Praluent. Amgen also seeks a judgment of patent infringement of the asserted patents, monetary damages (together with interest), costs and expenses of the lawsuits, and attorneys' fees. A jury trial in this litigation was held in the United States District Court for the District of Delaware (the "District Court") from March 8 to March 16, 2016. During the course of the trial, the District Court ruled as a matter of law in favor of Amgen that the asserted patent claims were not obvious, and in favor of the Company and the Sanofi defendants that there was no willful infringement of the asserted patent claims by the Company or the Sanofi defendants. On March 16, 2016, the jury returned a verdict in favor of Amgen, finding that the asserted claims of the '165 and '741 Patents were not invalid based on either a lack of written description or a lack of enablement. On January 3, 2017, the District Court issued a final opinion and judgment, denying the Company and the Sanofi defendants' motions for new trial and judgment as a matter of law. The District Court also denied as moot Amgen's motion to strike the Company and the Sanofi defendants' request to obtain a judgment as a matter of law, which allowed the United States Court of Appeals for the Federal Circuit (the "Federal Circuit") to address the Company and the Sanofi defendants' patent invalidity arguments on appeal. On January 12, 2017, the Company and the Sanofi defendants filed a notice of appeal with the Federal Circuit. On April 19, 2017, the District Court granted Amgen's motion to amend the judgment on an accounting of supplemental damages and enhancement of such damages if deemed appropriate, but deferred the order until after the Federal Circuit issued a decision on the appeal. Oral argument on the appeal was held on June 6, 2017. On October 5, 2017, the Federal Circuit reversed in part the District Court's decision, remanded for a new trial on the issues of written description and enablement, and, as discussed below, vacated the District Court's permanent injunction. In addition, it affirmed the District Court's ruling that Amgen's patents were not obvious. The Federal Circuit further concluded the Company and the Sanofi defendants were not entitled to judgment as a matter of law on the issues of written description and enablement on this record. On January 5, 2017, the District Court granted a permanent injunction prohibiting Regeneron and the Sanofi defendants from Commercializing Praluent in the United States but subsequently delayed its imposition until February 21, 2017. The Federal Circuit stayed the injunction pending appeal on February 8, 2017 and vacated it on October 5, 2017. On July 25, 2016, Amgen filed a lawsuit against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi-Synthelabo Limited, Aventis Pharma Limited, Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the English High Court of Justice, Chancery Division, Patents Court, in London, seeking a declaration of infringement of Amgen's European Patent No. 2,215,124 (the "'124 Patent"), which pertains to PCSK9 monoclonal antibodies, by Praluent. The lawsuit also seeks a permanent injunction, damages, an accounting of profits, and costs and interest. On February 8, 2017, the court temporarily stayed this litigation on terms mutually agreed by the parties. Also on July 25, 2016, Amgen filed a lawsuit for infringement of the '124 Patent against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the Regional Court of Düsseldorf, Germany, seeking a permanent injunction, an accounting of marketing activities, a recall of Praluent and its removal from distribution channels, and damages. Oral hearing on this infringement lawsuit was held on October 19, 2017. On September 26, 2016, Amgen filed a lawsuit for infringement of the '124 Patent in the Tribunal de grande instance in Paris, France against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie, and Sanofi Chimie (subsequently added as a defendant). Amgen is seeking the prohibition of allegedly infringing activities with a €10,000 penalty per drug unit of Praluent produced in violation of the court order sought by Amgen; an appointment of an expert for the assessment of damages; disclosure of technical (including supply-chain) and accounting information to the expert and the court; provisional damages of €10.0 million (which would be awarded on an interim basis pending final determination); reimbursement of costs; publication of the ruling in three newspapers; and provisional enforcement of the decision to be issued, which would ensure enforcement of the decision (including any provisional damages) pending appeal. Amgen is not seeking a preliminary injunction in this proceeding at this time. On April 10, 2017, the Company and the Sanofi parties filed briefs seeking invalidation of certain of the claims of the '124 Patent, and Amgen filed a response on July 28, 2017. Oral hearing on this infringement lawsuit is currently scheduled for June 29, 2018. The '124 Patent is also subject to opposition proceedings in the European Patent Office seeking to invalidate certain of its claims, which were initiated by the Company on November 24, 2016. On May 19, 2017, Amgen filed a lawsuit for infringement of Amgen's Japanese Patent Nos. 5,906,333 (the "'333 Patent") and 5,705,288 (the "'288 Patent") in the Tokyo District Court Civil Division against Sanofi K.K. Amgen's complaint alleges that manufacturing, selling or otherwise transferring, and offering to sell or otherwise transfer Praluent (alirocumab) in Japan (as well as importing Praluent (alirocumab) into Japan) infringe the '333 and '288 Patents. The complaint further seeks a permanent injunction, disposal of product, and court costs. The Company has not been named as a defendant in this litigation. At this time, the Company is not able to predict the outcome of, or estimate a range of possible loss, if any, related to these proceedings. Proceedings Relating to Dupixent (dupilumab) Injection On March 20, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation filed a complaint against Amgen and Immunex Corporation, a wholly owned subsidiary of Amgen, in the United States District Court for the District of Massachusetts seeking a declaratory judgment that the Company's and the other plaintiffs' commercializing of Dupixent does not directly or indirectly infringe U.S. Patent No. 8,679,487 (the "'487 Patent") owned by Immunex Corporation relating to antibodies that bind the human interleukin-4 receptor. On May 1, 2017, the Company and the other plaintiffs filed a notice of voluntary dismissal of this action without prejudice. On March 23, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation initiated an inter partes review ("IPR") in the United States Patent and Trademark Office ("USPTO") seeking a declaration of invalidity of the '487 Patent. On July 28 and 31, 2017, the same parties filed two additional IPR petitions in the USPTO seeking declarations of invalidity of the '487 Patent based on different grounds (the "Additional IPR Petitions"). On October 4, 2017, the Patent Trial and Appeal Board of the USPTO issued a decision on the first IPR petition and declined to institute an IPR proceeding to review the validity of the '487 Patent. The Additional IPR Petitions are still pending. On April 5, 2017, Immunex Corporation filed a complaint against the Company, Sanofi, Sanofi-Aventis U.S. LLC, Genzyme Corporation, and Aventisub LLC in the United States District Court for the Central District of California seeking a judgment of patent infringement of the '487 Patent and a declaratory judgment of infringement of the '487 Patent, in each case by the Company's and the other defendants' Commercializing of Dupixent; monetary damages (together with interest); an order of willful infringement of the '487 Patent, which would allow the court in its discretion to award damages up to three times the amount assessed; costs and expenses of the lawsuit; and attorneys' fees. Immunex is not seeking an injunction in this proceeding at this time. On June 21, 2017, the court denied a motion to dismiss Immunex's complaint previously filed by the Company and the Sanofi parties. On June 28, 2017, the Company and the Sanofi parties filed an answer to Immunex's complaint and counterclaims against Immunex and Amgen (which was amended on October 31, 2017 to, among other things, add an inequitable conduct allegation), and Immunex and Amgen filed an answer to the counterclaims on July 28, 2017. A jury trial has been scheduled to start on March 19, 2019. At this time, the Company is not able to predict the outcome of, or estimate a range of possible loss, if any, related to these proceedings. Proceedings Relating to Shareholder Derivative Claims On December 30, 2015, an alleged shareholder filed a shareholder derivative complaint in the New York Supreme Court, naming the then current and certain former non-employee members of the Company's board of directors, the Chairman of the board of directors, the Company's Chief Executive Officer, and the Company's Chief Scientific Officer as defendants and Regeneron as a nominal defendant. The complaint asserts that the individual defendants breached their fiduciary duties and were unjustly enriched when they approved and/or received allegedly excessive compensation in 2013 and 2014. The complaint seeks damages in favor of the Company for the alleged breaches of fiduciary duties and unjust enrichment; changes to Regeneron's corporate governance and internal procedures; invalidation of the Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan with respect to the individual defendants' compensation and a shareholder vote regarding the individual defendants' equity compensation; equitable relief, including an equitable accounting with disgorgement; and award of the costs of the action, including attorneys' fees. On June 28, 2017, the court dismissed the plaintiff's claims with respect to certain compensation awarded in 2013 but denied the defendants' motion to dismiss the other claims set forth in the complaint. On or about December 15, 2015, the Company received a shareholder litigation demand upon the Company's board of directors made by a purported Regeneron shareholder. On or about November 3, 2017, the Company received a second shareholder litigation demand upon the Company's board of directors made by another purported Regeneron shareholder, which is substantially similar to the December 15, 2015 shareholder litigation demand. The demands assert that the then current and certain former non-employee members of the board of directors and the Chairman of the board of directors excessively compensated themselves in 2013 and 2014. The demands request that the board of directors investigate and bring legal action against these directors for breach of fiduciary duty, unjust enrichment, and corporate waste, and implement internal controls and systems designed to prohibit and prevent similar actions in the future. The Company's board of directors is evaluating the impact of the court's decision pertaining to the motion to dismiss discussed above on the board's response to these demands. At this time, the Company is not able to predict the outcome of, or estimate a range of possible loss, if any, relating to these matters. Department of Justice Investigation In January 2017, the Company received a subpoena from the U.S. Attorney's Office for the District of Massachusetts requesting documents relating to its support of 501(c)(3) organizations that provide financial assistance to patients; documents concerning its provision of financial assistance to patients with respect to products sold or developed by Regeneron (including EYLEA, Praluent, ARCALYST, and ZALTRAP^®); and certain other related documents and communications. The Company is cooperating with this investigation. The Company cannot predict the outcome or duration of this investigation or any other legal proceedings or any enforcement actions or other remedies that may be imposed on the Company arising out of this investigation.

Recently Issued Accounting Standards (Notes)	9 Months Ended
Recently Issued Accounting Standards (Notes)	Sep. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Recently Issued Accounting Standards In May 2014, the FASB issued Accounting Standards Update 2014-09 ("ASU 2014-09"), Revenue from Contracts with Customers, which, along with subsequent amendments to ASU 2014-09 issued by the FASB, will replace existing revenue recognition guidance. The new standard requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. To achieve that core principle, an entity must identify the contract(s) with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies the performance obligation. The new standard will be effective for annual and interim reporting periods beginning after December 15, 2017. Early adoption is permitted, but no earlier than 2017 for calendar year-end entities. The standard allows for two transition methods - retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial adoption (modified retrospective method). The Company has substantially completed its impact assessment, and does not currently expect the new standard to have a material impact on total revenues. However, substantive development milestones, which were previously recognized in the period when the milestone was achieved, will be recognized over the remaining performance period under the new standard. In connection with adopting the new standard, the Company does not anticipate implementing changes to its systems or internal controls. The Company expects to adopt the standard using the modified retrospective method, and continues to evaluate the impact of the new guidance on its financial statement disclosures. In January 2016, the FASB issued Accounting Standards Update 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. The amendments require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. The implementation of the amendments is expected to increase the volatility of the Company's net income, as the Company holds publicly traded equity investments; however, the Company is not able to estimate the impact of adopting these amendments, as the significance of the impact will depend on the Company's equity investment balance upon adoption. In February 2016, the FASB issued Accounting Standards Update 2016-02, Leases. The new standard requires a lessee to recognize in its balance sheet (for both finance and operating leases) a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The Company is currently evaluating the impact that this guidance will have on the Company's financial statements, including related disclosures. The Company expects the new standard will have a significant impact on its internal controls, systems, and processes. In August 2017, the FASB issued Accounting Standard Update 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities. The amendments expand and refine hedge accounting for both financial and non-financial risk components, align the recognition and presentation of the effects of hedging instruments and hedge items in the financial statements, and include certain targeted improvements to ease the application of current guidance related to the assessment of hedge effectiveness. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The Company does not expect the implementation of the amendments to have an impact on the Company's financial statements in connection with its current derivative instruments.

Net Product Sales (Policies)	9 Months Ended
Net Product Sales (Policies)	Sep. 30, 2017
Revenues [Abstract]
Revenue Recognition, Revenue Reductions [Policy Text Block]	Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks, distribution-related fees, and other sales-related deductions.

Legal Matters (Policies)	9 Months Ended
Legal Matters (Policies)	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Legal Costs, Policy [Policy Text Block]	Costs associated with the Company's involvement in legal proceedings are expensed as incurred.

Net Product Sales (Tables)

9 Months Ended

Sep. 30, 2017

Revenue from External Customer [Line Items]

Revenue from External Customers by Products and Services [Table Text Block]



	Three Months Ended September 30,				Nine Months Ended September 30,
Net Product Sales in the United States	2017		2016		2017		2016
EYLEA^®	$	953,279	$	853,588	$	2,727,132	$	2,465,369
ARCALYST^®	4,088		3,880		12,613		10,500
Net Product Sales	$	957,367	$	857,468	$	2,739,745	$	2,475,869

Schedules of Concentration of Risk, by Risk Factor [Table Text Block]



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Besse Medical, a subsidiary of AmerisourceBergen Corporation	51	%	54	%	51	%	56	%
McKesson Corporation	29	%	28	%	29	%	28	%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts	19	%	17	%	19	%	15	%

Sales Related Deductions Activity

The following table summarizes the provisions and credits/payments for these sales-related deductions during the nine months ended September 30, 2017 and 2016.



	Rebates & Chargebacks			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2016	$	12,712		$	29,465		$	3,674		$	45,851
Provisions	121,599			140,860			33,518			295,977
Credits/payments	(108,811		)	(136,272		)	(21,444		)	(266,527		)
Balance as of September 30, 2017	$	25,500		$	34,053		$	15,748		$	75,301

Balance as of December 31, 2015	$	6,419		$	48,313		$	517		$	55,249
Provisions	63,510			113,755			22,812			200,077
Credits/payments	(62,503		)	(135,483		)	(19,587		)	(217,573		)
Balance as of September 30, 2016	$	7,426		$	26,585		$	3,742		$	37,753

Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2017

Collaboration Agreement [Abstract]

Collaboration revenue with related party

The collaboration revenue the Company earned from Sanofi is detailed below:



	Three Months Ended September 30,						Nine Months Ended September 30,
Sanofi Collaboration Revenue	2017			2016			2017			2016
Antibody:
Reimbursement of Regeneron research and development expenses	$	128,539		$	131,389		$	421,056		$	469,223
Reimbursement of Regeneron commercialization-related expenses	90,339			64,418			251,002			213,957
Regeneron's share of losses in connection with commercialization of antibodies	(98,315		)	(112,001		)	(328,998		)	(333,530		)
Other	41,848			4,360			84,338			19,999
Total Antibody	162,411			88,166			427,398			369,649
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	61,649			36,226			188,408			97,851
Other	21,115			20,000			61,864			60,000
Total Immuno-oncology	82,764			56,226			250,272			157,851
	$	245,175		$	144,392		$	677,670		$	527,500

Collaboration revenue

The collaboration revenue the Company earned from Bayer is detailed below:



	Three Months Ended September 30,				Nine Months Ended September 30,
Bayer Collaboration Revenue	2017		2016		2017		2016
EYLEA:
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	205,367	$	170,854	$	571,126	$	484,181
Reimbursement of Regeneron EYLEA development expenses	6,053		2,219		10,833		7,186
Other	15,714		6,077		36,910		45,924
Total EYLEA	227,134		179,150		618,869		537,291
Ang2 antibody and PDGFR-beta antibody:
Reimbursement of development expenses	7,325		7,433		15,614		14,165
Other	2,166		4,715		6,436		11,330
Total Ang2 antibody and PDGFR-beta antibody	9,491		12,148		22,050		25,495
	$	236,625	$	191,298	$	640,919	$	562,786

Net Income Per Share (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Basic and Diluted Net Income (Loss) Per Share

The calculations of basic and diluted net income per share are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Net income - basic	$	388,317	$	264,804	$	1,024,992	$	642,407
Effect of dilutive securities:
Convertible senior notes - interest expense and amortization of discount and note issuance costs	—		—		—		397
Net income - diluted	$	388,317	$	264,804	$	1,024,992	$	642,804

(Shares in thousands)
Weighted average shares - basic	106,706		104,833		106,108		104,586
Effect of dilutive securities:
Stock options	9,809		10,156		9,386		10,340
Restricted stock	513		479		500		474
Convertible senior notes	—		—		—		81
Warrants	—		998		—		1,086
Dilutive potential shares	10,322		11,633		9,886		11,981
Weighted average shares - diluted	117,028		116,466		115,994		116,567

Net income per share - basic	$	3.64	$	2.53	$	9.66	$	6.14
Net income per share - diluted	$	3.32	$	2.27	$	8.84	$	5.51

Antidilutive Securities

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive include the following:



	Three Months Ended September 30,		Nine Months Ended September 30,
(Shares in thousands)	2017	2016	2017	2016
Stock options	4,515	7,687	8,892	7,842
Restricted stock	—	19	—	19
Convertible senior notes	—	3	—	—

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The following tables summarize the Company's investments in marketable securities:



	Amortized		Unrealized					Fair
As of September 30, 2017	Cost Basis		Gains		Losses			Value
Corporate bonds	$	1,564,391	$	2,789	$	(2,691	)	$	1,564,489
U.S. government and government agency obligations	189,647		56		(645		)	189,058
Municipal bonds	4,614		—		(8		)	4,606
Commercial paper	61,464		—		—			61,464
Certificates of deposit	6,525		—		—			6,525
Equity securities	57,251		30,789		—			88,040
	$	1,883,892	$	33,634	$	(3,344	)	$	1,914,182

As of December 31, 2016
Corporate bonds	$	1,076,964	$	630	$	(4,743	)	$	1,072,851
U.S. government and government agency obligations	132,923		58		(641		)	132,340
Municipal bonds	7,663		1		(20		)	7,644
Commercial paper	63,074		1		—			63,075
Certificates of deposit	42,612		—		—			42,612
Equity securities	57,251		5,551		(13,583		)	49,219
	$	1,380,487	$	6,241	$	(18,987	)	$	1,367,741

Marketable Securities, Based on Contractual Maturity Dates

The fair values of debt security investments by contractual maturity consist of the following:



	September 30, 2017		December 31, 2016
Maturities within one year	$	586,879	$	503,481
Maturities after one year through five years	1,239,263		815,041
	$	1,826,142	$	1,318,522

Fair Value and Unrealized Losses of Marketable Securities



	Less than 12 Months					12 Months or Greater					Total
As of September 30, 2017	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	675,374	$	(2,111	)	$	110,545	$	(580	)	$	785,919	$	(2,691	)
U.S. government and government agency obligations	141,393		(591		)	6,943		(54		)	148,336		(645		)
Municipal bonds	4,105		(8		)	—		—			4,105		(8		)
	$	820,872	$	(2,710	)	$	117,488	$	(634	)	$	938,360	$	(3,344	)

As of December 31, 2016
Corporate bonds	$	759,222	$	(4,685	)	$	36,407	$	(58	)	$	795,629	$	(4,743	)
U.S. government and government agency obligations	81,170		(641		)	—		—			81,170		(641		)
Municipal bonds	7,141		(20		)	—		—			7,141		(20		)
Equity securities	36,417		(13,583		)	—		—			36,417		(13,583		)
	$	883,950	$	(18,929	)	$	36,407	$	(58	)	$	920,357	$	(18,987	)

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Schedule of assets measured at fair value on a recurring basis

The Company's assets that are measured at fair value on a recurring basis consist of the following:



			Fair Value Measurements at Reporting Date Using
As of September 30, 2017	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Corporate bonds	$	1,564,489	—		$	1,564,489
U.S. government and government agency obligations	189,058		—		189,058
Municipal bonds	4,606		—		4,606
Commercial paper	61,464		—		61,464
Certificates of deposit	6,525		—		6,525
Equity securities	88,040		$	88,040	—
	$	1,914,182	$	88,040	$	1,826,142

As of December 31, 2016
Available-for-sale marketable securities:
Corporate bonds	$	1,072,851	—		$	1,072,851
U.S. government and government agency obligations	132,340		—		132,340
Municipal bonds	7,644		—		7,644
Commercial paper	63,075		—		63,075
Certificates of deposit	42,612		—		42,612
Equity securities	49,219		$	49,219	—
	$	1,367,741	$	49,219	$	1,318,522

Inventory (Tables)

9 Months Ended

Sep. 30, 2017

Inventory Disclosure [Abstract]

Schedule of Inventory, Current

Inventories consist of the following:



	September 30,		December 31,
	2017		2016
Raw materials	$	187,029	$	92,287
Work-in-process	217,448		202,301
Finished goods	23,958		13,334
Deferred costs	213,153		91,434
	$	641,588	$	399,356

Accounts Payable and Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2017

Payables and Accruals [Abstract]

Schedule of Accounts Payable and Accrued Liabilities

Accounts payable and accrued expenses consist of the following:



	September 30,		December 31,
	2017		2016
Accounts payable	$	153,946	$	134,984
Accrued payroll and related costs	166,102		153,086
Accrued clinical trial expenses	119,608		91,753
Accrued sales-related charges, deductions, and royalties	167,467		159,985
Income taxes payable	126,612		235,776
Other accrued expenses and liabilities	84,691		103,512
	$	818,426	$	879,096

Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 2017

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]

The following table summarizes the notional amounts of the Company's outstanding interest rate swap and cap agreements as of September 30, 2017:



	Notional Amount
Interest rate swap contracts	$	75,000
Interest rate cap contracts	$	75,000

Net Product Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Net Product Sales (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Revenue Disclosure [Line Items]
Net product sales	$ 957,367	$ 857,468	$ 2,739,745	$ 2,475,869
Activity of Sales Related Deductions [Roll Forward]
Balance	75,301	37,753	75,301	37,753	$ 45,851	$ 55,249
Provision related to current period sales			295,977	200,077
Credits/payments			(266,527)	(217,573)
Rebates and Chargebacks
Activity of Sales Related Deductions [Roll Forward]
Balance	25,500	7,426	25,500	7,426	12,712	6,419
Provision related to current period sales			121,599	63,510
Credits/payments			(108,811)	(62,503)
Distribution Related Fees
Activity of Sales Related Deductions [Roll Forward]
Balance	34,053	26,585	34,053	26,585	29,465	48,313
Provision related to current period sales			140,860	113,755
Credits/payments			(136,272)	(135,483)
Other Sales Related Deductions
Activity of Sales Related Deductions [Roll Forward]
Balance	$ 15,748	$ 3,742	15,748	3,742	$ 3,674	$ 517
Provision related to current period sales			33,518	22,812
Credits/payments			$ (21,444)	$ (19,587)
Besse Medical [Member] \| Customer concentration risk \| Gross Sales Revenue
Risks and Uncertainties [Abstract]
Concentration risk, percentage	51.00%	54.00%	51.00%	56.00%
EYLEA
Revenue Disclosure [Line Items]
Net product sales	$ 953,279	$ 853,588	$ 2,727,132	$ 2,465,369
ARCALYST
Revenue Disclosure [Line Items]
Net product sales	$ 4,088	$ 3,880	$ 12,613	$ 10,500
McKesson Corporation [Member] \| Customer concentration risk \| Gross Sales Revenue
Risks and Uncertainties [Abstract]
Concentration risk, percentage	29.00%	28.00%	29.00%	28.00%
Curascript SD [Member] \| Customer concentration risk \| Gross Sales Revenue
Risks and Uncertainties [Abstract]
Concentration risk, percentage	19.00%	17.00%	19.00%	15.00%
Minimum [Member] \| Customer concentration risk \| Gross Sales Revenue
Risks and Uncertainties [Abstract]
Concentration risk, percentage	10.00%	10.00%	10.00%	10.00%

Collaboration Agreements (Sanofi) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Collaboration Agreement [Line Items]
Revenue from Related Parties		$ 245,175	$ 144,392			$ 677,670	$ 527,500
Research and development		529,749	543,047			1,547,159	1,573,089
Deferred Revenue From Related Party Current		187,036				187,036			$ 115,267
Antibody Collaboration
Collaboration Agreement [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement		(98,315)	(112,001)			(328,998)	(333,530)
Reimbursement of Regeneron research and development expenses		128,539	131,389			421,056	469,223
Reimbursement Revenue		90,339	64,418			251,002	213,957
Contracts Revenue		41,848	4,360			84,338	19,999
Revenue from Related Parties		162,411	88,166			$ 427,398	369,649
Percentage of Trial Costs borne by collaborating party						80.00%
Percentage of Trial Costs borne by entity						20.00%
IO Discovery Agreement
Collaboration Agreement [Line Items]
Annual Funding Maximum of Research Activities Per Agreement						$ 200,000
IO Agreement
Collaboration Agreement [Line Items]
Deferred Revenue, Additions					$ 640,000
Immuno-oncology Agreement
Collaboration Agreement [Line Items]
Reimbursement of Regeneron research and development expenses		61,649	36,226			188,408	97,851
Contracts Revenue		21,115	20,000			61,864	60,000
Revenue from Related Parties		82,764	56,226			250,272	157,851
Praluent, Kevzara, and Dupixent [Member] [Member] \| Antibody Collaboration
Collaboration Agreement [Line Items]
Research and development		$ 22,600	$ 27,900			$ 68,200	$ 80,200
Scenario, Forecast [Member] \| Antibody Collaboration
Collaboration Agreement [Line Items]
Annual funding maximum of research activities per amended agreement								$ 130,000
Mitsubishi Tanabe Pharma Corporation (MTPC) [Member] \| Collaborative Arrangement [Member]
Collaboration Agreement [Line Items]
Deferred Revenue, Additions	$ 10,000
Additional payments received [Member] [Member] \| Mitsubishi Tanabe Pharma Corporation (MTPC) [Member] \| Collaborative Arrangement [Member]
Collaboration Agreement [Line Items]
Deferred Revenue, Additions				$ 60,000

Collaboration Agreements (Bayer) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaboration Agreement [Line Items]
Other Collaboration Revenue	$ 236,625	$ 191,298	$ 640,919	$ 562,786
EYLEA
Collaboration Agreement [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement	205,367	170,854	571,126	484,181
Reimbursement of Regeneron research and development expenses	6,053	2,219	10,833	7,186
Contracts Revenue	15,714	6,077	36,910	45,924
Other Collaboration Revenue	227,134	179,150	618,869	537,291
Ang2 antibody and PDGFR-beta antibody
Collaboration Agreement [Line Items]
Reimbursement of Regeneron research and development expenses	7,325	7,433	15,614	14,165
Contracts Revenue	2,166	4,715	6,436	11,330
Other Collaboration Revenue	$ 9,491	$ 12,148	$ 22,050	$ 25,495

Collaboration Agreements (EYLEA) (Details) - Collaboration Agreement with Bayer	9 Months Ended
	Sep. 30, 2017
Minimum [Member]
Collaboration Agreement [Line Items]
Revenue based on percentage of annual sales in Japan	33.50%
Maximum [Member]
Collaboration Agreement [Line Items]
Revenue based on percentage of annual sales in Japan	40.00%

Collaboration Agreements (Ang2 Antibody) (Details) - Ang2 Antibody $ in Millions	Mar. 31, 2016 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred Revenue, Additions	$ 50.0
Percentage of global development cost to be paid by the collaboration partner under the collaboration	25.00%
Percentage of development cost for the territory outside the United States to be paid for under the collaboration	50.00%

Collaboration Agreements (Mitsubishi Tanabe Pharma) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Jun. 30, 2017	Mar. 31, 2016	Sep. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Document Period End Date				Sep. 30, 2017
Mitsubishi Tanabe Pharma Corporation (MTPC) \| Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue, Additions	$ 10.0
Revenue Recognition, Milestone Method, Revenue Recognized		$ 30.0
Mitsubishi Tanabe Pharma Corporation (MTPC) \| Collaborative Arrangement [Member] \| Additional payments received [Member] [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue, Additions			$ 60.0

Collaboration Agreements Teva Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		$ 1,500,673		$ 1,220,122	$ 4,289,780	$ 3,633,600
Teva Pharmaceuticals [Member] \| Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue, Additions	$ 250,000
Revenues		$ 40,200		$ 5,200	$ 141,000
Revenue Recognition, Milestone Method, Revenue Recognized			$ 25,000

Collaboration Agreements (Intella Therapeutics) (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended	9 Months Ended
	Apr. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments to Acquire Marketable Securities			$ 883,748	$ 606,153
Collaborative Arrangement [Member] \| Intellia Therapeutics [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Other Research and Development Expense	$ 75,000
Payments to Acquire Marketable Securities		$ 50,000

Collaboration Agreements Adicet Bio (Details) - Adicet Bio [Member] - Collaborative Arrangement [Member] $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Other Research and Development Expense	$ 25.0
Research and Development Arrangement, Contract to Perform for Others, Description and Terms	5

Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 388,317	$ 264,804	$ 1,024,992	$ 642,407
Interest on Convertible Debt, Net of Tax	0	0	0	397
Net Income (Loss) Available to Common Stockholders, Diluted	$ 388,317	$ 264,804	$ 1,024,992	$ 642,804
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic	106,706	104,833	106,108	104,586
Effect of dilutive securities (in shares):
Stock options	9,809	10,156	9,386	10,340
Restricted stock	513	479	500	474
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	0	0	0	81
Warrants	0	998	0	1,086
Dilutive potential shares	10,322	11,633	9,886	11,981
Weighted average shares - diluted (in shares)	117,028	116,466	115,994	116,567
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 3.64	$ 2.53	$ 9.66	$ 6.14
Net income per share - diluted (in dollars per share)	$ 3.32	$ 2.27	$ 8.84	$ 5.51
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	4,515	7,687	8,892	7,842
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	0	19	0	19
Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares	0	3	0	0

Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities, Realized Gain (Loss)	$ 0	$ 0	$ 0	$ 0
Amortized Cost Basis	1,883,892		1,883,892		$ 1,380,487
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	33,634		33,634		6,241
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,344)		(3,344)		(18,987)
Available-for-sale Securities	1,914,182		1,914,182		1,367,741
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Maturities within one year	586,879		586,879		503,481
Maturities after one year through five years	1,239,263		1,239,263		815,041
Total	1,826,142		1,826,142		1,318,522
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	820,872		820,872		883,950
Fair Value - 12 Months or Greater	117,488		117,488		36,407
Fair Value - Total	938,360		938,360		920,357
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(2,710)		(2,710)		(18,929)
Unrealized Loss - 12 Months or Greater	(634)		(634)		(58)
Unrealized Loss - Total	(3,344)		(3,344)		(18,987)
Corporate Bond Securities [Member]
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	675,374		675,374		759,222
Fair Value - 12 Months or Greater	110,545		110,545		36,407
Fair Value - Total	785,919		785,919		795,629
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(2,111)		(2,111)		(4,685)
Unrealized Loss - 12 Months or Greater	(580)		(580)		(58)
Unrealized Loss - Total	(2,691)		(2,691)		(4,743)
U.S. government and government agency obligations
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	141,393		141,393		81,170
Fair Value - 12 Months or Greater	6,943		6,943		0
Fair Value - Total	148,336		148,336		81,170
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(591)		(591)		(641)
Unrealized Loss - 12 Months or Greater	(54)		(54)		0
Unrealized Loss - Total	(645)		(645)		(641)
Municipal bonds
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	4,105		4,105		7,141
Fair Value - 12 Months or Greater	0		0		0
Fair Value - Total	4,105		4,105		7,141
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(8)		(8)		(20)
Unrealized Loss - 12 Months or Greater	0		0		0
Unrealized Loss - Total	(8)		(8)		(20)
Equity Securities
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months					36,417
Fair Value - 12 Months or Greater					0
Fair Value - Total					36,417
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months					(13,583)
Unrealized Loss - 12 Months or Greater					0
Unrealized Loss - Total					(13,583)
Unrestricted [Member] \| Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	1,564,391		1,564,391		1,076,964
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,789		2,789		630
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2,691)		(2,691)		(4,743)
Available-for-sale Securities	1,564,489		1,564,489		1,072,851
Unrestricted [Member] \| U.S. government and government agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	189,647		189,647		132,923
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	56		56		58
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(645)		(645)		(641)
Available-for-sale Securities	189,058		189,058		132,340
Unrestricted [Member] \| Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	4,614		4,614		7,663
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0		0		1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(8)		(8)		(20)
Available-for-sale Securities	4,606		4,606		7,644
Unrestricted [Member] \| Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	61,464		61,464		63,074
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0		0		1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0		0		0
Available-for-sale Securities	61,464		61,464		63,075
Unrestricted [Member] \| Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	6,525		6,525		42,612
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0		0		0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0		0		0
Available-for-sale Securities	6,525		6,525		42,612
Unrestricted [Member] \| Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	57,251		57,251		57,251
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	30,789		30,789		5,551
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0		0		(13,583)
Available-for-sale Securities	$ 88,040		$ 88,040		$ 49,219

Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0		$ 0
Proceeds from Sale and Maturity of Marketable Securities			379,275	$ 192,091
Payments to Acquire Marketable Securities			883,748	606,153
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	$ 0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	0
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	1,914,182		1,914,182		$ 1,367,741
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other than Temporary Impairment Losses, Investments	0	0	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from Sale and Maturity of Marketable Securities	0	0	0	0
Payments to Acquire Marketable Securities	0	0	0	0
Marketable Securities, Unrealized Gain (Loss)	0	$ 0	0	$ 0
Measured on a recurring basis \| Fair Value, Inputs, Level 1 [Member]
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	88,040		88,040		49,219
Measured on a recurring basis \| Fair Value, Inputs, Level 2 [Member]
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	1,826,142		1,826,142		1,318,522
Measured on a recurring basis \| Unrestricted [Member] \| Fair Value, Inputs, Level 1 [Member]
Available-for-sale marketable securities:
Corporate bonds	0		0		0
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	0		0		0
Municipal bonds	0		0		0
Commercial Paper	0		0		0
Certificates of Deposit, at Carrying Value	0		0		0
Equity securities	88,040		88,040		49,219
Measured on a recurring basis \| Unrestricted [Member] \| Fair Value, Inputs, Level 2 [Member]
Available-for-sale marketable securities:
Corporate bonds	1,564,489		1,564,489		1,072,851
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	189,058		189,058		132,340
Municipal bonds	4,606		4,606		7,644
Commercial Paper	61,464		61,464		63,075
Certificates of Deposit, at Carrying Value	6,525		6,525		42,612
Equity securities	0		0		0
Estimate of Fair Value Measurement [Member] \| Measured on a recurring basis
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	1,914,182		1,914,182		1,367,741
Estimate of Fair Value Measurement [Member] \| Measured on a recurring basis \| Unrestricted [Member]
Available-for-sale marketable securities:
Corporate bonds	1,564,489		1,564,489		1,072,851
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	189,058		189,058		132,340
Municipal bonds	4,606		4,606		7,644
Commercial Paper	61,464		61,464		63,075
Certificates of Deposit, at Carrying Value	6,525		6,525		42,612
Equity securities	$ 88,040		$ 88,040		$ 49,219

Inventory (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Inventory [Line Items]
Raw materials	$ 187,029		$ 187,029		$ 92,287
Work in process	217,448		217,448		202,301
Finished goods	23,958		23,958		13,334
Deferred costs	213,153		213,153		91,434
Total Inventories	641,588		641,588		$ 399,356
Inventory Write-down	$ 5,400	$ 5,000	$ 14,500	$ 11,300

Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accounts payable	$ 153,946	$ 134,984
Accrued payroll and related costs	166,102	153,086
Accrued clinical trial expense	119,608	91,753
Accrued sales-related charges, deductions and royalties	167,467	159,985
Taxes Payable, Current	126,612	235,776
Other accrued expenses and liabilities	84,691	103,512
Accounts payable and accrued expenses	$ 818,426	$ 879,096

Debt (Details) - USD ($)	3 Months Ended	9 Months Ended
Debt (Details) - USD ($)	Mar. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Repayments of convertible senior notes		$ 0	$ (12,650,000)
Treasury Stock, Shares		3,763,868		3,763,868
Treasury Stock, Value		$ 316,240,000		$ 316,240,000
Payments in connection with deduction of outstanding warrants		0	242,117,000
Credit Facility [Domain]
Line of Credit Facility, Maximum Borrowing Capacity	$ 750,000,000
Line of Credit Facility, Expiration Period	5 years
Line of Credit Facility, Fair Value of Amount Outstanding		$ 0
Convertible senior notes
Debt Conversion			12,700,000
Repayments of convertible senior notes			$ (12,700,000)
Stock Issued During Period, Shares, New Issues			118,822
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			$ 47,100,000
Treasury Stock, Shares			118,808
Treasury Stock, Value			$ 10,000,000
November 2015 Agreement [Member]
Limit price per share for warrant holders to close out hedge position			$ 535.00
Payments in connection with deduction of outstanding warrants			$ 135,200,000
Reduction of number of warrants			360,406
February 2016 Agreement [Member]
Payments in connection with deduction of outstanding warrants			$ 106,900,000
Reduction of number of warrants			403,665
Limit price per share for warrant holders to close out hedge position pursuant to the agreement			$ 375.00

Leases (Details) - USD ($) $ in Millions	3 Months Ended
Leases (Details) - USD ($) $ in Millions	Jun. 30, 2017	Mar. 31, 2017	Mar. 03, 2017	Dec. 31, 2016	Dec. 30, 2016
Capital Leased Assets [Line Items]
Facility Purchase Price					$ 720.0
Payment towards purchase price of Tarrytown facility				$ 57.0
Aggregate funding advanced to the participants			$ 720.0
Reimbursement received by the Company			57.0
Initial term of lease		5 years
Potential extended term of lease		5 years
Tarrytown facility capital and facility Lease obligations			$ 720.0
Tarrytown lease transaction [Member]
Capital Leased Assets [Line Items]
Out of period adjustment	$ 30.1

Derivative Instruments (Details) - USD ($)	3 Months Ended		9 Months Ended
Derivative Instruments (Details) - USD ($)	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2017
Derivative [Line Items]
Initial term of lease		5 years
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness	$ 0		$ 0
Interest Rate Swap Contracts
Derivative [Line Items]
Derivative, Notional Amount	75,000,000		75,000,000
Interest Rate Cap Contracts
Derivative [Line Items]
Derivative, Notional Amount	$ 75,000,000		$ 75,000,000

Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
Income Taxes (Details) - USD ($)	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Total income tax expense (benefit)	$ 177,288,000	$ 101,077,000	$ 498,752,000	$ 345,881,000
Document Period End Date			Sep. 30, 2017
Effective income tax rate	31.30%	27.60%	32.70%	35.00%
Available-for-sale Securities, Income Tax Expense on Change in Unrealized Holding Gain (Loss)	$ (6,400,000.0)		$ (6,500,000.0)	$ 3,300,000

Statement of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
Statement of Cash Flows (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Accrued capital expenditures	$ 24.5	$ 33.9	$ 28.2	$ 50.7
Capital Lease Obligations Incurred	$ 201.2	$ 0.0

Legal Matters (Details)	9 Months Ended
Legal Matters (Details)	Sep. 30, 2017 EUR (€)
Loss Contingencies [Line Items]
Loss Contingency, Damages Sought, per unit produced.	€ 10,000
Loss Contingency, Damages Sought, Value	€ 10,000,000