Regeneron Pharmaceuticals (REGN) 10-K 12 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jun. 30, 2014	Feb. 05, 2015
Entity Information [Line Items]
Entity Registrant Name	REGENERON PHARMACEUTICALS INC
Entity Central Index Key	872589
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$27,323,000,000
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding			100,645,094
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding			1,971,868

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$648,719	$535,608
Marketable securities	251,761	158,376
Accounts receivable - trade, net	739,379	787,071
Accounts receivable from Sanofi	121,058	104,707
Accounts receivable from Bayer HealthCare	156,962	63,189
Inventories	128,861	70,354
Deferred tax assets	49,235	44,677
Prepaid expenses and other current assets	71,486	32,952
Total current assets	2,167,461	1,796,934
Marketable securities	460,154	389,891
Property, plant, and equipment, at cost, net of accumulated depreciation and amortization	974,309	526,983
Deferred tax assets	266,869	231,878
Other assets	3,034	5,327
Total assets	3,871,827	2,951,013
Current liabilities:
Accounts payable and accrued expenses	484,228	250,896
Deferred revenue from Sanofi, current portion	15,927	12,815
Deferred revenue - other, current portion	58,098	34,185
Other current liabilities	96,407	939
Total current liabilities	654,660	298,835
Deferred revenue from Sanofi	72,367	76,522
Deferred revenue - other	103,909	107,677
Facility lease obligations	310,938	184,258
Convertible senior notes	146,773	320,315
Other long term liabilities	40,855	11,330
Total liabilities	1,329,502	998,937
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred Stock	0	0
Additional paid-in capital	2,404,118	2,045,857
Retained earnings (accumulated deficit)	255,382	-92,692
Accumulated other comprehensive income (loss)	52,251	-1,188
Treasury Stock, Value	-169,530	0
Total stockholders' equity	2,542,325	1,952,076
Total liabilities and stockholders' equity	3,871,827	2,951,013
Class A Stock
Stockholders' equity:
Common stock	2	2
Total stockholders' equity	2	2
Common Stock
Stockholders' equity:
Common stock	102	97
Total stockholders' equity	$102	$97

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
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)	2,017,732	0
Class A Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$0.00	$0.00
Common Stock, shares authorized (in shares)	40,000,000	40,000,000
Common Stock, shares issued (in shares)	1,973,368	2,020,481
Common Stock, shares outstanding (in shares)	1,973,368	2,020,481
Common Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$0.00	$0.00
Common Stock, shares authorized (in shares)	160,000,000	160,000,000
Common Stock, shares issued (in shares)	102,475,154	97,666,814

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Net product sales	$1,750,762	$1,425,839	$858,093
Sanofi collaboration revenue	541,299	430,111	423,814
Bayer HealthCare collaboration revenue	495,555	220,289	70,099
Technology licensing and other revenue	31,941	28,506	26,471
Total revenues	2,819,557	2,104,745	1,378,477
Expenses:
Research and development	1,271,353	859,947	625,554
Selling, general, and administrative	504,755	329,415	210,755
Cost of goods sold	129,030	118,048	83,927
Cost of collaboration manufacturing	75,988	37,307	528
Total expenses	1,981,126	1,344,717	920,764
Income from operations	838,431	760,028	457,713
Other income (expense):
Investment and other income (expense)	8,157	-231	2,012
Interest expense	-37,372	-46,437	-45,304
Loss on Extinguishment of Debt	-33,469	0	0
Total other income (expense)	-62,684	-46,668	-43,292
Income before income taxes	775,747	713,360	414,421
Income tax (expense) benefit	-427,673	-288,998	335,848
Net income	348,074	424,362	750,269
Net income per share - basic	$3.46	$4.33	$7.92
Net income per share - diluted	$3.07	$3.81	$6.75
Weighted average shares outstanding - basic	100,612	97,917	94,685
Weighted average shares outstanding - diluted	113,413	111,290	115,382
Statements of Comprehensive Income
Net income	348,074	424,362	750,269
Other comprehensive income:
Unrealized gain (loss) on marketable securities, net of tax	53,439	-22	696
Comprehensive income	$401,513	$424,340	$750,965

CONSOLIDATED_STATEMENTS_OF_STO

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Total	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Common Class A	Common Stock
In Thousands, except Share data, unless otherwise specified
Balance at Dec. 31, 2011	$485,732	$1,754,824	($1,267,323)	$0	($1,862)	$2	$91
Balance (shares) at Dec. 31, 2011				0		2,109,000	90,692,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options	67,174	67,169					5
Issuance of Common Stock in connection with exercise of stock options (shares)							5,086,000
Common Stock tendered upon exercise of stock options in connection with employee tax obligations	-112,834	-112,833					-1
Common Stock tendered upon exercise of stock options in connection with employee tax obligations (in shares)							-878,000
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	6,325	6,325
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (shares)							64,000
Issuance of restricted Common Stock under Long-Term Incentive Plan	0
Issuance of restricted Common Stock under Long-Term Incentive Plan (shares)							501,000
Restricted Common Stock tendered upon vesting in connection with employee tax obligations	-50,466	-50,466
Restricted Common Stock rendered upon vesting in connection with employee tax obligations (in shares)							-282,000
Conversion of Class A Stock to Common Stock (shares)						-40,000	40,000
Stock-based compensation charges	94,181	94,181
Excess tax benefit from stock-based compensation	4,308	4,308
Net income	750,269		750,269
Other comprehensive income (loss), net of tax	696				696
Balance at Dec. 31, 2012	1,245,385	1,763,508	-517,054	0	-1,166	2	95
Balance (shares) at Dec. 31, 2012				0		2,069,000	95,223,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options	54,762	54,759					3
Issuance of Common Stock in connection with exercise of stock options (shares)							3,052,000
Common Stock tendered upon exercise of stock options in connection with employee tax obligations	-179,423	-179,422					-1
Common Stock tendered upon exercise of stock options in connection with employee tax obligations (in shares)							-644,000
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	5,718	5,718
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (shares)							38,000
Issuance of restricted Common Stock under Long-Term Incentive Plan	0
Issuance of restricted Common Stock under Long-Term Incentive Plan (shares)							6,000
Restricted Common Stock tendered upon vesting in connection with employee tax obligations	-15,664	-15,664
Restricted Common Stock rendered upon vesting in connection with employee tax obligations (in shares)							-57,000
Conversion of Class A Stock to Common Stock (shares)						-49,000	49,000
Stock-based compensation charges	200,101	200,101
Excess tax benefit from stock-based compensation	216,857	216,857
Net income	424,362		424,362
Other comprehensive income (loss), net of tax	-22				-22
Balance at Dec. 31, 2013	1,952,076	2,045,857	-92,692	0	-1,188	2	97
Balance (shares) at Dec. 31, 2013				0		2,020,000	97,667,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options	125,897	125,893					4
Issuance of Common Stock in connection with exercise of stock options (shares)							3,468,000
Common Stock tendered upon exercise of stock options in connection with employee tax obligations	-267,584	-267,583					-1
Common Stock tendered upon exercise of stock options in connection with employee tax obligations (in shares)							-754,000
Issuance of Common Stock in connection with conversion of convertible senior notes	691,356	691,354					2
Issuance of Common Stock in connection with conversion of convertible senior notes (in shares)							2,018,000
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	13,125	13,125
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (shares)							21,000
Issuance of restricted Common Stock under Long-Term Incentive Plan	0
Issuance of restricted Common Stock under Long-Term Incentive Plan (shares)							8,000
Conversion of Class A Stock to Common Stock (shares)						-47,000	47,000
Stock-based compensation charges	312,303	312,303
Excess tax benefit from stock-based compensation	448,556	448,556
Acquisition of Common Stock in connection with exercise of convertible note hedges	0	169,530		-169,530
Acquisition of Common Stock in connection with exercise of convertible note hedges (in shares)				-2,018,000
Reduction of warrants	-294,552	-294,552
Reclassification of warrant liability	-148,496	-148,496
Reduction of equity component of convertible senior notes	-691,869	-691,869
Net income	348,074
Other comprehensive income (loss), net of tax	53,439				53,439
Shares, Issued							102,475,000
Balance at Dec. 31, 2014	$2,542,325	$2,404,118	$255,382	($169,530)	$52,251	$2	$102
Balance (shares) at Dec. 31, 2014				-2,018,000		1,973,000

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$348,074	$424,362	$750,269
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	52,686	41,204	36,940
Non-cash compensation expense	307,238	198,399	94,157
Non-cash interest expense	18,052	23,061	22,925
Loss on Extinguishment of Debt	33,469	0	0
Other non-cash charges and expenses, net	30,003	23,690	34,049
Increase (Decrease) in Deferred Income Taxes	-66,604	63,601	-340,156
Changes in assets and liabilites
Increase in Sanofi, Bayer HealthCare, and trade accounts receivable	-62,432	-258,994	-588,398
Increase in Inventories	-60,900	-47,956	-28,932
(Increase) decrease in prepaid expenses and other assets	-37,767	7,571	-25,371
Increase (decrease) in deferred revenue	19,102	-27,974	-41,077
Increase in accounts payable, accrued expenses and other liabilities	162,236	136,684	10,979
Total adjustments	395,083	159,286	-824,884
Net cash provided by (used in) operating activities	743,157	583,648	-74,615
Cash flows from investing activities:
Purchases of marketable securities	-564,188	-577,278	-470,945
Sales or maturities of marketable securities	476,417	378,146	439,209
Capital expenditures	-333,006	-156,323	-49,337
Net cash used in by investing activities	-420,777	-355,455	-81,073
Cash flows from financing activities:
Payments in connection with facility and capital lease obligations	-1,095	-2,024	-2,203
Repayments of convertible senior debt	-220,639	0	0
Payments in connection with reduction of outstanding warrants	-294,552	0	0
Proceeds from issuance of Common Stock	126,045	57,393	63,549
Payments in connection with Common Stock tendered for employee tax obligations	-267,584	-195,087	-163,300
Excess tax benefit from stock-based compensation	448,556	216,857	4,308
Net cash (used in) provided by financing activities	-209,269	77,139	-97,646
Net increase (decrease) in cash and cash equivalents	113,111	305,332	-253,334
Cash and cash equivalents at beginning of period	535,608	230,276	483,610
Cash and cash equivalents at end of period	648,719	535,608	230,276
Supplemental disclosure of cash flow information
Cash paid for interest (net of amounts capitalized)	20,614	23,842	21,946
Cash paid for income taxes	$59,847	$1,057	$0

Organization_and_Business

Organization and Business	12 Months Ended
	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Business	Organization and Business
	Regeneron Pharmaceuticals, Inc. and its subsidiaries (collectively, the "Company" or "Regeneron") is a fully integrated biopharmaceutical company that discovers, invents, develops, manufactures, and commercializes medicines for the treatment of serious medical conditions. The Company has product candidates in development in areas of high unmet medical need, including hypercholesterolemia, oncology, rheumatoid arthritis, asthma, and atopic dermatitis. The Company is a party to collaboration agreements to develop certain of these product candidates (see Note 4). The Company also currently has three marketed products:
	•	EYLEA® (aflibercept) Injection, known in the scientific literature as VEGF Trap-Eye, which is available in the United States, European Union ("EU"), Japan, and certain other countries outside the United States for the treatment of neovascular age-related macular degeneration ("wet AMD"), macular edema following central retinal vein occlusion ("CRVO"), and diabetic macular edema ("DME"). In addition, EYLEA for the treatment of macular edema following retinal vein occlusion ("RVO"), which includes macular edema following branch retinal vein occlusion ("BRVO"), is available in the United States, and EYLEA for the treatment of myopic choroidal neovascularization ("mCNV") is available in Japan. Bayer HealthCare has additional regulatory applications for various indications pending in other countries. The Company is collaborating with Bayer HealthCare on the global development and commercialization of EYLEA outside the United States. The Company maintains exclusive rights to EYLEA in the United States and is entitled to all profits from such sales.
	•	ZALTRAP® (ziv-aflibercept) Injection for Intravenous Infusion, known in the scientific literature as VEGF Trap, which is available in the United States, EU, and certain other countries for treatment, in combination with 5-fluorouracil, leucovorin, irinotecan ("FOLFIRI"), for patients with metastatic colorectal cancer ("mCRC") that is resistant to or has progressed following an oxaliplatin-containing regimen. Regeneron and Sanofi globally collaborate on the development and commercialization of ZALTRAP.
	•	ARCALYST® (rilonacept) Injection for Subcutaneous Use, which is available in the United States for the treatment of Cryopyrin-Associated Periodic Syndromes ("CAPS"), including Familial Cold Auto-inflammatory Syndrome ("FCAS") and Muckle-Wells Syndrome ("MWS"), in adults and children 12 and older.
	The Company operates in one business segment, which includes all activities related to the discovery, development, and commercialization of pharmaceutical products for the treatment of serious medical conditions. The Company's business is subject to certain risks including, but not limited to, uncertainties relating to conducting pharmaceutical research, product development, obtaining regulatory approvals, market acceptance, competition, and obtaining and enforcing patents.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
	Basis of Presentation
	The consolidated financial statements include the accounts of Regeneron and its wholly-owned subsidiaries. Intercompany balances and transactions are eliminated in consolidation.
	Use of Estimates
	The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Estimates which could have a significant impact on the Company's financial statements include provisions related to product sales, such as rebates, chargebacks, and distribution-related fees; periods over which payments, including non-refundable up-front, license, and milestone payments, are recognized as revenue in connection with collaboration and other agreements; periods over which certain clinical trial costs are recognized; fair value of stock options; inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value; capitalization of inventory costs associated with the Company's products prior to regulatory approval; deferred tax asset valuation allowance; and the assessment of uncertain tax positions.
	With respect to the Company's collaborations with Sanofi and Bayer HealthCare:
	•	Included in Sanofi collaboration revenue is the Company's share of profits or losses from commercialization of ZALTRAP and commercialization of antibodies, which are provided by Sanofi, and include an estimate of the Company's share of profits or losses for the most recent fiscal quarter.
	•	Included in Bayer HealthCare collaboration revenue is the Company's share of profits or losses from commercialization of EYLEA outside the United States, which is provided by Bayer HealthCare, and includes an estimate of the Company's share of profits or losses for the most recent fiscal quarter.
	•	Included in research and development expenses is the Company's share of development expenses incurred by its collaborators, Bayer HealthCare and Sanofi, including the Company's share of Bayer HealthCare and Sanofi estimated development expenses for the most recent fiscal quarter.
	These estimates for the most recent period are adjusted, if necessary, in the subsequent period to reflect actual amounts.
	Cash and Cash Equivalents
	The Company considers all highly liquid debt instruments with a maturity of three months or less when purchased to be cash equivalents. The carrying amount reported in the Balance Sheet for cash and cash equivalents approximates its fair value.
	Marketable Securities
	The Company has an investment policy that includes guidelines on acceptable investment securities, minimum credit quality, maturity parameters, and concentration and diversification. The Company invests its excess cash primarily in marketable securities issued by investment grade institutions. The Company considers its marketable securities to be "available-for-sale," as defined by authoritative guidance issued by the Financial Accounting Standards Board ("FASB"). These assets are carried at fair value and the unrealized gains and losses are included in accumulated other comprehensive income (loss). If a decline in the value of a marketable security in the Company's investment portfolio is deemed to be other-than-temporary, the Company writes down the security to its current fair value and recognizes a loss as a charge against income. The Company reviews its portfolio of marketable securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost are other-than-temporary.
	Accounts Receivable - Trade
	The Company's trade accounts receivable arise from product sales and represent amounts due from its distributors and specialty pharmacies (collectively, the Company's "customers"), which are all located in the United States. The Company monitors the financial performance and credit worthiness of its large customers so that it can properly assess and respond to changes in their credit profile. The Company provides reserves against trade receivables for estimated losses, if any, that may result from a customer's inability to pay. Amounts determined to be uncollectible are written-off against the reserve.
	Inventories
	Inventories are stated at the lower of cost or estimated realizable value. The Company determines the cost of inventory using the first-in, first-out, or FIFO, method.
	The Company capitalizes inventory costs associated with the Company's products prior to regulatory approval when, based on management's judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed as research and development. The determination to capitalize inventory costs is based on various factors, including status and expectations of the regulatory approval process, any known safety or efficacy concerns, potential labeling restrictions, and any other impediments to obtaining regulatory approval.
	The Company periodically analyzes its inventory levels to identify inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value, and writes-down such inventories as appropriate. In addition, the Company's products are subject to strict quality control and monitoring which the Company performs throughout the manufacturing process. If certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, the Company records a charge to cost of goods sold to write down such unmarketable inventory to its estimated realizable value.
	Property, Plant, and Equipment
	Property, plant, and equipment are stated at cost, net of accumulated depreciation. Depreciation is provided on a straight-line basis over the estimated useful lives of the assets. Costs of construction of certain long-lived assets include capitalized interest, which is amortized over the estimated useful life of the related asset. Expenditures for maintenance and repairs which do not materially extend the useful lives of the assets are charged to expense as incurred. The cost and accumulated depreciation or amortization of assets retired or sold are removed from the respective accounts, and any gain or loss is recognized in operations. The estimated useful lives of property, plant, and equipment are as follows:
	Building and improvements		10-30 years
	Laboratory and other equipment		3-10 years
	Furniture and fixtures		5 years
	The Company periodically assesses the recoverability of long-lived assets, such as property, plant, and equipment, and evaluates such assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Asset impairment is determined to exist if estimated future undiscounted cash flows are less than the carrying amount.
	Revenue Recognition
	a. Product Revenue
	Product sales consist of U.S. sales of EYLEA and ARCALYST. Revenue from product sales is recognized when persuasive evidence of an arrangement exists, title to product and associated risk of loss have passed to the customer, the price is fixed or determinable, collection from the customer is reasonably assured, the Company has no further performance obligations, and returns can be reasonably estimated. The Company's written contracts with its customers stipulate product is shipped freight on board destination (FOB destination). The Company records revenue from product sales upon delivery to its customers.
	The Company sells EYLEA in the United States to several distributors and specialty pharmacies. The Company sells ARCALYST in the United States to two specialty pharmacies. Under these distribution models, the distributors and specialty pharmacies generally take physical delivery of product. For EYLEA, the distributors and specialty pharmacies generally sell the product directly to healthcare providers, whereas for ARCALYST, the specialty pharmacies sell the product directly to patients.
	Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks under governmental programs, distribution-related fees, prompt pay discounts, product returns, and other sales-related deductions. Calculating these provisions involves estimates and judgments. The Company reviews its estimates of rebates, chargebacks, and other applicable provisions each period and records any necessary adjustments in the current period's net product sales.
	Government Rebates and Chargebacks: The Company estimates reductions to product sales for Medicaid and Veterans' Administration ("VA") programs, and for certain other qualifying federal and state government programs. Based upon the Company's contracts with government agencies, statutorily-defined discounts applicable to government-funded programs, historical experience, and estimated payer mix, the Company estimates and records an allowance for rebates and chargebacks. The Company's liability for Medicaid rebates consists of estimates for claims that a state will make for a current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, and invoices received for claims from prior quarters that have not been paid. The Company's reserves related to discounted pricing to VA, Public Health Services ("PHS"), and other institutions (collectively "qualified healthcare providers") represent the Company's estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices the Company charges to its customers (i.e., distributors and specialty pharmacies). The Company's customers charge the Company for the difference between what they pay for the products and the ultimate selling price to the qualified healthcare providers. The Company's reserve for this discounted pricing is based on expected sales to qualified healthcare providers and the chargebacks that customers have already claimed.
	Distribution-Related Fees: The Company has written contracts with its customers that include terms for distribution-related fees. The Company estimates and records distribution and related fees due to its customers based on gross sales.
	Prompt Pay Discounts: No prompt pay discounts are currently offered to the Company's customers on sales of EYLEA. In connection with sales of ARCALYST, the Company offers discounts to its customers for prompt payments. The Company estimates these discounts based on customer terms and historical experience, and expects that its customers will always take advantage of this discount. Therefore, the Company accrues 100% of the prompt pay discount that is based on the gross amount of each ARCALYST invoice, at the time of sale.
	Product Returns: Consistent with industry practice, the Company offers its customers a limited right to return product purchased directly from the Company, which is principally based upon the product's expiration date. The Company will accept returns for three months prior to and up to six months after the product expiration date. Product returned is generally not resalable given the nature of the Company's products and method of administration. The Company develops estimates for product returns based upon historical experience, inventory levels in the distribution channel, shelf life of the product, and other relevant factors. The Company monitors product supply levels in the distribution channel, as well as sales by its customers of EYLEA to healthcare providers and ARCALYST to patients using product-specific data provided by its customers. If necessary, the Company's estimates of product returns may be adjusted in the future based on actual returns experience, known or expected changes in the marketplace, or other factors.
	b. Collaboration Revenue
	The Company earns collaboration revenue in connection with collaboration agreements to develop and commercialize product candidates and utilize the Company's technology platforms. These arrangements may require the Company to deliver various rights, services, and/or goods across the entire life cycle of a product or product candidate. The terms of these agreements typically include that consideration be provided to the Company in the form of non-refundable up-front licensing payments, research progress (milestone) payments, payments for development and commercialization activities, and sharing of profits or losses arising from the commercialization of products. In arrangements involving multiple deliverables, each required deliverable is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is generally based on whether the deliverables in the arrangement meet certain criteria, including whether the delivered item or items has value to the collaborator on a standalone basis. The arrangement's consideration that is fixed and determinable is allocated to each separate unit of accounting based on the relative selling price of each deliverable. If multiple collaboration activities or rights do not require separation, they are combined into a single unit of accounting and recognized over the performance period, which is the period over which the Company is obligated to deliver goods or services. Historically, non-refundable up-front license payments, where continuing involvement is required of the Company, have been deferred and recognized over the related performance period. The Company estimates its performance period based on the specific terms of each agreement, and adjusts the performance periods, if appropriate, based on the applicable facts and circumstances. Payments which are based on achieving a specific substantive performance milestone, involving a degree of risk, are recognized as revenue when the milestone is achieved and the related payment is due and non-refundable, provided there is no future service obligation associated with that milestone. Substantive performance milestones typically consist of significant achievements in the development life-cycle of the related product candidate, such as completion of clinical trials, filing for approval with regulatory agencies, and receipt of approvals by regulatory agencies. In determining whether a payment is deemed to be a substantive performance milestone, the Company takes into consideration (i) the enhancement in value to the related development product candidate, (ii) the Company's performance and the relative level of effort required to achieve the milestone, (iii) whether the milestone relates solely to past performance, and (iv) whether the milestone payment is considered reasonable relative to all of the deliverables and payment terms. Payments for achieving milestones which are not considered substantive are deferred and recognized over the related performance period.
	The Company enters into collaboration agreements that include varying arrangements regarding which parties perform and bear the costs of research and development activities. The Company may share the costs of research and development activities with a collaborator, or the Company may be reimbursed for all or a significant portion of the costs of the Company's research and development activities. The Company records its internal and third-party development costs associated with these collaborations as research and development expenses. When the Company is entitled to reimbursement of all or a portion of the research and development expenses that it incurs under a collaboration, the Company records those reimbursable amounts as collaboration revenue proportionately as the Company recognizes its expenses. If the collaboration is a cost-sharing arrangement in which both the Company and its collaborator perform development work and share costs, the Company also recognizes, as additional research and development expense in the period when its collaborator incurs development expenses, the portion of the collaborator's development expenses that the Company is obligated to reimburse. The Company may also be obligated to use commercially reasonable efforts to supply commercial bulk product to its collaborators. In such cases, the Company is reimbursed for its manufacturing costs as commercial product is shipped to its collaborators; however, recognition of such cost reimbursements as collaboration revenue is deferred until the product is sold by the Company's collaborators to third-party customers, at which time the Company's risk of inventory loss no longer exists. In addition, at that time, the related manufacturing costs for the sold product, which had been capitalized into inventory, are recognized by the Company.
	Under the Company's collaboration agreements, product sales and cost of sales for products which are currently approved are recorded by the Company's collaborators. The Company shares in any profits or losses arising from the commercialization of such products. The Company records its share of the profits or losses from commercialization of such products, representing net product sales less cost of goods sold and shared commercialization and other expenses, as collaboration revenue.
	In connection with non-refundable licensing payments, the Company's performance period estimates are principally based on projections of the scope, progress, and results of its research and development activities. Due to the variability in the scope of activities and length of time necessary to develop a drug product, changes to development plans as programs progress, and uncertainty in the ultimate requirements to obtain governmental approval for commercialization, revisions to performance period estimates are likely to occur periodically, and could result in material changes to the amount of revenue recognized each year in the future. In addition, estimated performance periods may change if development programs encounter delays, or the Company and its collaborators decide to expand or contract the clinical plans for a drug candidate in various disease indications.
	c. VelocImmune® Technology Licensing
	The Company enters into non-exclusive license agreements with third parties that allow the third party to utilize the Company's VelocImmune technology in its internal research programs. The terms of these agreements may include up-front payments and entitle the Company to receive royalties on any future sales of products discovered by the third party using the Company's VelocImmune technology. Up-front payments under these agreements, where continuing involvement is required of the Company, are deferred and recognized ratably over their respective license periods.
	Research and Development Expenses
	Research and development expenses include costs directly attributable to the conduct of research and development programs, including the cost of salaries, payroll taxes, employee benefits, materials, supplies, depreciation on and maintenance of research equipment, costs related to research collaboration and licensing agreements, the cost of services provided by outside contractors, including services related to the Company's clinical trials, clinical trial expenses, the full cost of manufacturing drug for use in research, preclinical development, and clinical trials, amounts that the Company is obligated to reimburse to collaborators for research and development expenses that they incur, and the allocable portions of facility costs, such as rent, utilities, insurance, repairs and maintenance, depreciation, and general support services. All costs associated with research and development are expensed.
	Clinical trial costs are a significant component of research and development expenses and include costs associated with third-party contractors. The Company outsources a substantial portion of its clinical trial activities, utilizing external entities such as contract research organizations ("CROs"), independent clinical investigators, and other third-party service providers to assist the Company with the execution of its clinical studies. For each clinical trial that the Company conducts, certain clinical trial costs are expensed immediately, while others are expensed over time based on the expected total number of patients in the trial, the rate at which patients enter the trial, and/or the period over which clinical investigators or CROs are expected to provide services.
	Clinical activities which relate principally to clinical sites and other administrative functions to manage the Company's clinical trials are performed primarily by CROs. CROs typically perform most of the start-up activities for the Company's trials, including document preparation, site identification, screening and preparation, pre-study visits, training, and program management. These start-up costs usually occur within a few months after the contract has been executed and are event driven in nature. The remaining activities and related costs, such as patient monitoring and administration, generally occur ratably throughout the life of the individual contract or study. In the event of early termination of a clinical trial, the Company accrues and recognizes expenses in an amount based on its estimate of the remaining non-cancelable obligations associated with the winding down of the clinical trial and/or penalties.
	For clinical study sites, where payments are made periodically on a per-patient basis to the institutions performing the clinical study, the Company accrues expenses on an estimated cost-per-patient basis, based on subject enrollment and activity in each quarter. The amount of clinical study expense recognized in a quarter may vary from period to period based on the duration and progress of the study, the activities to be performed by the sites each quarter, the required level of patient enrollment, the rate at which patients actually enroll in and drop-out of the clinical study, and the number of sites involved in the study. Clinical trials that bear the greatest risk of change in estimates are typically those that have a significant number of sites, require a large number of patients, have complex patient screening requirements, and span multiple years. During the course of a trial, the Company adjusts its rate of clinical expense recognition if actual results differ from the Company's estimates. The Company's estimates and assumptions for clinical expense recognition could differ significantly from its actual results, which could cause material increases or decreases in research and development expenses in future periods when the actual results become known.
	Stock-based Compensation
	The Company recognizes stock-based compensation expense for grants of stock option awards and restricted stock under the Company's Long-Term Incentive Plan to employees and non-employee members of the Company's board of directors based on the grant-date fair value of those awards. The grant-date fair value of an award is generally recognized as compensation expense over the award's requisite service period. In addition, the Company has granted performance-based stock option awards which vest based upon the optionee satisfying certain performance and service conditions as defined in the agreements. Potential compensation cost, measured on the grant date, related to these performance options will be recognized only if, and when, the Company estimates that these options will vest, which is based on whether the Company considers the options' performance conditions to be probable of attainment. The Company's estimates of the number of performance-based options that will vest will be revised, if necessary, in subsequent periods.
	The Company uses the Black-Scholes model to compute the estimated fair value of stock option awards. Using this model, fair value is calculated based on assumptions with respect to (i) expected volatility of the Company's Common Stock price, (ii) the periods of time over which employees and members of the board of directors are expected to hold their options prior to exercise (expected lives), (iii) expected dividend yield on the Common Stock, and (iv) risk-free interest rates. Stock-based compensation expense also includes an estimate, which is made at the time of grant, of the number of awards that are expected to be forfeited. This estimate is revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	Income Taxes
	The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined on the basis of the difference between the tax basis of assets and liabilities and their respective financial reporting amounts ("temporary differences") at enacted tax rates in effect for the years in which the differences are expected to reverse. A valuation allowance is established for deferred tax assets for which it is more likely than not that some portion or all of the deferred tax assets will not be realized.
	Uncertain tax positions are accounted for in accordance with FASB authoritative guidance, which prescribes a comprehensive model for the manner in which a company should recognize, measure, present, and disclose in its financial statements all material uncertain tax positions that the company has taken or expects to take on a tax return. Those positions, for which management's assessment is that there is more than a 50% probability of sustaining the position upon challenge by a taxing authority based upon its technical merits, are subjected to certain measurement criteria.
	The Company's policy is to recognize interest and penalties related to income tax matters in income tax expense.
	Per Share Data
	Basic net income per share is 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. Basic net income per share excludes restricted stock awards until vested. Diluted net income per share includes the potential dilutive effect of common stock equivalents as if such securities were converted or exercised during the period, when the effect is dilutive. Common stock equivalents include: (i) outstanding stock options and restricted stock awards under the Company's Long-Term Incentive Plans, which are included under the "treasury stock method" when dilutive, (ii) Common Stock to be issued upon the assumed conversion of the Company's convertible senior notes, which are included under the "if-converted method" when dilutive, and (iii) Common Stock to be issued upon the exercise of outstanding warrants, which are included under the "treasury stock method" when dilutive.
	Concentration of Credit Risk
	Financial instruments which potentially expose the Company to concentrations of credit risk consist of cash, cash equivalents, certain financial instruments, and accounts receivable. A large portion of the Company's cash is held by a few major financial institutions. In accordance with the Company's policies, the Company mandates asset diversification and monitors exposure with its counterparties.
	Concentrations of credit risk with respect to accounts receivable are significant. Accounts receivable from product sales of EYLEA and ARCALYST are due from several distributors and specialty pharmacies, who are the Company's customers. As of December 31, 2014 and 2013, one individual customer accounted for 70% and 75%, respectively, of the Company's net trade accounts receivable balances. The Company has contractual payment terms with each of its customers, and the Company monitors its customers' financial performance and credit worthiness so that it can properly assess and respond to any changes in their credit profile. In addition, the Company may insure a portion of its accounts receivables within its overall risk management practices. As of December 31, 2014 and 2013, there were no reserves against trade accounts receivable. In addition, during the years ended December 31, 2014, 2013, and 2012, the Company did not recognize any charges for write-offs of trade accounts receivable.
	Reclassifications
	Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.
	Recently Issued Accounting Standards
	In May 2014, the FASB issued a new standard related to revenue recognition, Revenue from Contracts with Customers, which 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, 2016, and early adoption is not permitted. The standard allows for two transition methods - retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial adoption. The Company has not yet determined its method of transition and is evaluating the impact that this guidance will have on the Company's financial statements.

Net_Product_Sales

Net Product Sales	12 Months Ended
	Dec. 31, 2014
Revenues [Abstract]
Net Product Sales	Product Sales
	The Company received marketing approval from the U.S. Food and Drug Administration (FDA) for EYLEA (aflibercept) Injection for the treatment of wet AMD in November 2011, for the treatment of macular edema following CRVO in September 2012, for the treatment of DME in July 2014, and for the treatment of macular edema following RVO, which includes macular edema following BRVO, in October 2014. EYLEA net product sales in the United States totaled $1,736.4 million, $1,408.7 million, and $837.9 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	In February 2008, the Company received marketing approval from the FDA for ARCALYST Injection for Subcutaneous Use for the treatment of CAPS. ARCALYST net product sales totaled $14.4 million, $17.1 million, and $20.2 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	For the years ended December 31, 2014, 2013, and 2012, the Company recorded 73%, 76%, and 78%, respectively, of its total gross product revenue from sales to Besse Medical, a subsidiary of AmerisourceBergen Corporation.
	Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks under governmental programs, distribution-related fees, prompt pay discounts, and other sales-related deductions. The following table summarizes the provisions, and credits/payments, for these sales-related deductions for the years ended December 31, 2014, 2013, and 2012.
		Rebates &			Distribution-			Other Sales-			Total
		Chargebacks			Related			Related
					Fees			Deductions
	Balance as of December 31, 2011	$	585		$	1,451		$	182		$	2,218
	Provision related to current period sales	14,153			45,028			3,070			62,251
	Credits/payments	(11,755		)	(31,181		)	(2,707		)	(45,643		)
	Balance as of December 31, 2012	2,983			15,298			545			18,826
	Provision related to current period sales	25,936			62,984			955			89,875
	Credits/payments	(24,519		)	(58,619		)	(962		)	(84,100		)
	Balance as of December 31, 2013	4,400			19,663			538			24,601
	Provision related to current period sales	33,117			77,160			1,578			111,855
	Credits/payments	(34,434		)	(75,657		)	(1,584		)	(111,675		)
	Balance as of December 31, 2014	$	3,083		$	21,166		$	532		$	24,781
	Under the provisions of the Patient Protection and Affordable Care Act ("PPACA") and the Health Care and Education Reconciliation Act of 2010, a non-tax deductible annual fee (the "Branded Prescription Drug Fee") is imposed on pharmaceutical manufacturers that sell branded prescription drugs to specified government programs. The legislation imposed an annual fee on companies for each calendar year beginning in 2011. This fee is allocated to companies based on their prior year market share of total branded prescription drug sales into these government programs. Orphan drugs sales, including ARCALYST, are not subject to the fee. In July 2014, the Internal Revenue Service ("IRS") issued final regulations that provide guidance on the Branded Prescription Drug Fee. The final regulations differ in some respects from the temporary regulations issued by the IRS in 2011, including that a company is liable for the fee based on its branded prescription drug sales in the current year, instead of the liability only being applicable upon the first qualifying branded prescription drug sale of the following fee year under the temporary regulations. As a result of the issuance of these final IRS regulations, the Company will record an estimate of the fee in the same period in which its qualifying branded prescription drug sales occur. Therefore, in the third quarter of 2014, an incremental charge was recorded to (i) recognize a liability for the estimated fee payable based on 2014 sales through the first nine months of 2014, and (ii) expense the remaining prepaid asset recorded under the previous accounting for the estimated fee payable based on 2013 sales. The impact of the incremental charge in the third quarter was $40.6 million, which was included in selling, general, and administrative expenses.

Collaboration_Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2014
Collaboration Agreement [Abstract]
Collaboration and Contract Research Agreements	Collaboration Agreements
	The Company has entered into various agreements related to its activities to research, develop, manufacture, and commercialize product candidates and utilize its technology platforms. Significant agreements of this kind are described below.
	a. Sanofi
	Sanofi owned a total of 22,859,144 shares of the Company's Common Stock as of December 31, 2014, a portion of which was purchased in connection with the companies' ZALTRAP and antibody collaborations described below. See Note 14 for a description of the investor agreement between Sanofi and the Company.
	The collaboration revenue the Company earned from Sanofi is detailed below:
		Year Ended December 31,
	Sanofi Collaboration Revenue	2014			2013			2012
	ZALTRAP:
	Regeneron's share of losses in connection with commercialization of ZALTRAP	$	(4,715	)	$	(30,810	)	$	(25,634	)
	Substantive milestone	—			—			50,000
	Reimbursement of Regeneron research and development expenses	4,806			5,639			10,702
	Other	5,102			9,682			13,268
	Total ZALTRAP	5,193			(15,489		)	48,336
	Antibody:
	Reimbursement of Regeneron research and development expenses	547,761			453,489			365,245
	Reimbursement of Regeneron commercialization-related expenses	19,480			1,868			—
	Regeneron's share of losses in connection with commercialization of antibodies	(41,378		)	—			—
	Up-front payments to Sanofi for acquisition of rights related to two antibodies	—			(20,000		)	—
	Other	10,243			10,243			10,233
	Total Antibody	536,106			445,600			375,478
		$	541,299		$	430,111		$	423,814
	ZALTRAP (aflibercept)
	In September 2003, the Company entered into a collaboration agreement (the "ZALTRAP Agreement") with Aventis Pharmaceuticals Inc. (predecessor to Sanofi U.S.), to jointly develop and commercialize ZALTRAP. In connection with this agreement, Sanofi made a non-refundable up-front payment of $80.0 million and purchased 2,799,552 newly issued unregistered shares of the Company's Common Stock for $45.0 million. In January 2005, the Company and Sanofi amended the ZALTRAP Agreement to exclude intraocular delivery of aflibercept to the eye ("Intraocular Delivery") from joint development under the agreement, and product rights to aflibercept in Intraocular Delivery reverted to Regeneron. In connection with this amendment, Sanofi made a $25.0 million non-refundable payment to Regeneron (the "Intraocular Termination Payment"). In December 2005, the Company and Sanofi amended the ZALTRAP Agreement to expand the territory in which the companies are collaborating on the development of ZALTRAP to include Japan. In connection with this amendment, Sanofi agreed to make a $25.0 million non-refundable up-front payment to the Company, which was received in January 2006.
	Sanofi commenced sales of ZALTRAP Injection for Intravenous Infusion, in combination with FOLFIRI, for patients with mCRC that is resistant to or has progressed following an oxaliplatin-containing regimen, in the United States in the third quarter of 2012 and in certain European and other countries in the first quarter of 2013. The Company earned, and recorded as revenue in 2012, a $50.0 million substantive milestone payment from Sanofi upon FDA approval of ZALTRAP. The Company currently manufactures clinical and commercial supplies of ZALTRAP.
	Under the ZALTRAP Agreement, as amended, the Company and Sanofi share co-promotion rights and profits and losses on sales of ZALTRAP outside of Japan, for disease indications included in the companies' collaboration. The Company is entitled to receive a percentage of approximately 35% on annual sales of ZALTRAP in Japan, subject to certain potential adjustments. According to the terms of the ZALTRAP Agreement, the Company may also receive up to $350 million in additional substantive milestone payments upon receipt of specified marketing approvals.
	Under the ZALTRAP Agreement, as amended, agreed upon worldwide development expenses incurred by both companies during the term of the agreement are funded by Sanofi. Regeneron is obligated to reimburse Sanofi out of its share of ZALTRAP profits, if any, for 50% of the development expenses that Sanofi funded, in accordance with a formula based on the amount of development expenses and Regeneron's share of collaboration profits, or at a faster rate at Regeneron's option. In connection with the January 2005 amendment to the ZALTRAP Agreement, the Intraocular Termination Payment of $25.0 million is also subject to 50% reimbursement by Regeneron to Sanofi if the collaboration is profitable. In particular, the Company's total contingent reimbursement obligation to Sanofi for ZALTRAP was approximately $461 million as of December 31, 2014. Regeneron has the option to conduct additional pre-Phase III studies at its own expense.
	Sanofi has the right to terminate the agreement without cause with at least twelve months advance notice. Upon termination of the agreement for any reason, Regeneron's obligation to reimburse Sanofi for 50% of ZALTRAP development expenses will terminate, and the Company will retain all rights to ZALTRAP.
	In accordance with the Company's revenue recognition policy described in Note 2, the up-front payments received in September 2003 and January 2006, of $80.0 million and $25.0 million, respectively, and reimbursement of Regeneron-incurred development expenses, are being recognized as collaboration revenue over the related performance period.
	In connection with the ZALTRAP Agreement, (i) at December 31, 2014, there was a net receivable of $10.5 million from Sanofi, and at December 31, 2013, there was a net payable of $1.4 million to Sanofi, and (ii) deferred revenue at December 31, 2014 and 2013 was $23.9 million and $18.2 million, respectively.
	Antibodies
	In November 2007, the Company entered into a global, strategic collaboration (the "Antibody Collaboration") with Sanofi to discover, develop, and commercialize fully human monoclonal antibodies. The Antibody Collaboration is governed by a Discovery and Preclinical Development Agreement (the "Discovery Agreement") and a License and Collaboration Agreement (the "License Agreement"). In connection with the execution of the Discovery Agreement in 2007, the Company received a non-refundable up-front payment of $85.0 million from Sanofi. In addition, under the Discovery Agreement, Sanofi is funding the Company's research to identify and validate potential drug discovery targets and develop fully human monoclonal antibodies against these targets. In November 2009, the Company and Sanofi amended these collaboration agreements to expand and extend the Antibody Collaboration. Pursuant to the Discovery Agreement, as amended, Sanofi agreed to fund up to $160 million per year of the Company's research activities in 2010 through 2017. Sanofi has an option to extend certain antibody development and preclinical activities relating to selected program targets for up to an additional three years after 2017.
	For each drug candidate identified under the Discovery Agreement, Sanofi has the option to license rights to the candidate under the License Agreement. If it elects to do so, Sanofi will co-develop the drug candidate with the Company through product approval. Under certain defined circumstances, upon exercising its option to license rights to particular candidates, Sanofi must make a $10 million substantive milestone payment to the Company. If Sanofi does not exercise its option to license rights to a particular drug candidate under the License Agreement, the Company retains the exclusive right to develop and commercialize such drug candidate, and Sanofi will receive a royalty on sales, if any. The Company and Sanofi are currently co-developing five therapeutic antibodies under the License Agreement.
	Under the License Agreement, agreed upon worldwide development expenses incurred by both companies during the term of the agreement 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, commencing in 2013, the Company recognized as additional research and development expense $109.7 million and $17.6 million in 2014 and 2013, respectively, of antibody development expenses that the Company was obligated to reimburse to Sanofi related to PRALUENTTM (alirocumab) and sarilumab. If the Antibody Collaboration becomes profitable, Regeneron will be obligated to reimburse Sanofi for 50% of worldwide development expenses that were fully funded by Sanofi and 30% of Shared Phase 3 Trial Costs, in accordance with a defined formula based on the amounts of these expenses and the Company's share of collaboration profits from commercialization of collaboration products. However, the Company is not required to apply more than 10% of its share of the profits from the antibody collaboration in any calendar quarter to reimburse Sanofi for these development costs. In particular, the Company's contingent reimbursement obligation to Sanofi was approximately $1,304 million as of December 31, 2014.
	Sanofi will lead commercialization activities for products developed under the License Agreement, subject to the Company's right to co-promote such products. The parties will equally share profits and losses from sales within the United States. The parties will share profits outside the United States on a sliding scale based on sales starting at 65% (Sanofi)/35% (Regeneron) and ending at 55% (Sanofi)/45% (Regeneron), and losses outside the United States at 55% (Sanofi)/45% (Regeneron). Effective in the second and fourth quarters of 2014, the Company and Sanofi began sharing pre-launch commercialization expenses related to PRALUENT and sarilumab, respectively. In addition to profit sharing, the Company is entitled to receive up to $250 million in sales milestone payments, with milestone payments commencing only if and after aggregate annual sales outside the United States exceed $1.0 billion on a rolling twelve-month basis.
	Regeneron is obligated to use commercially reasonable efforts to supply clinical requirements of each drug candidate under the Antibody Collaboration until commercial supplies of that drug candidate are being manufactured. In connection with the November 2009 amendment of the collaboration's Discovery Agreement, Sanofi funded $30.0 million of agreed-upon costs the Company incurred to expand its manufacturing capacity at its Rensselaer, New York facilities. Additionally, during 2014, Sanofi agreed to fund up to $17.5 million of agreed-upon 2014 and 2015 costs incurred by the Company in connection with expanding the Company's manufacturing capacity at its Rensselaer, New York facility.
	With respect to each antibody product which enters development under the License Agreement, Sanofi or the Company may, by giving twelve months' notice, opt-out of further development and/or commercialization of the product, in which event the other party retains exclusive rights to continue the development and/or commercialization of the product. The Company may also opt-out of the further development of an antibody product if it gives notice to Sanofi within thirty days of the date that Sanofi enters joint development of such antibody product under the License Agreement. Each of the Discovery Agreement and the License Agreement contains other termination provisions, including for material breach by the other party. Prior to December 31, 2017, Sanofi has the right to terminate the amended Discovery Agreement without cause with at least three months advance written notice; however, except under defined circumstances, Sanofi would be obligated to immediately pay to the Company the full amount of unpaid research funding during the remaining term of the research agreement through December 31, 2017. Upon termination of the collaboration in its entirety, the Company's obligation to reimburse Sanofi for development costs out of any future profits from collaboration products will terminate. Upon expiration of the amended Discovery Agreement, Sanofi has an option to license the Company's VelocImmune technology for an annual license fee plus royalties on any future sales of products developed using VelocImmune technology.
	In connection with the Antibody Collaboration, in August 2008, the Company entered into a separate agreement with Sanofi, which extended through December 2012, to use Regeneron's proprietary VelociGene® technology platform to supply Sanofi with genetically modified mammalian models of gene function and disease (the "VelociGene Agreement"). The VelociGene Agreement provided for minimum annual order quantities for the term of the agreement, for which the Company received payments totaling $21.5 million.
	In accordance with the Company's revenue recognition policy described in Note 2, the (i) $85.0 million up-front payment received in December 2007, (ii) reimbursement of Regeneron-incurred expenses under the Discovery and License Agreements, (iii) $21.5 million of aggregate minimum payments under the VelociGene Agreement, and (iv) reimbursement of agreed-upon costs to expand the Company's manufacturing capacity are being recognized as collaboration revenue over the related performance period.
	In May 2013, the Company acquired from Sanofi full exclusive rights to two families of novel antibodies invented at Regeneron and previously included in the Company's antibody collaboration with Sanofi. The Company acquired full rights to antibodies targeting the platelet derived growth factor (PDGF) family of receptors and ligands in ophthalmology and all other indications and to antibodies targeting the angiopoietin-2 (Ang2) receptor and ligand in ophthalmology. At the time of acquisition, antibodies to the PDGF receptor and Ang2 were in preclinical development for use in ophthalmology. With respect to PDGF antibodies, the Company made a $10.0 million up-front payment to Sanofi in 2013, as well as two $5.0 million development milestone payments to Sanofi in 2014 (which were recorded as research and development expense). The Company is also obligated to pay up to $30.0 million in additional potential development milestones as well as royalties on any future sales of PDGF antibodies. In addition, with respect to Ang2 antibodies in ophthalmology, the Company made a $10.0 million up-front payment to Sanofi in 2013.
	In July 2014, in connection with the Company's antibody collaboration with Sanofi, the Company purchased an FDA priority review voucher from a third party for $67.5 million. The Company and Sanofi equally shared the priority review voucher's purchase price, and the Company's share of the cost, or $33.8 million, was recorded as a research and development expense during the third quarter of 2014. The Company subsequently transferred the voucher to Sanofi, which used the priority review voucher in connection with the recent Biologics License Application submission to the FDA for PRALUENT.
	In connection with the Antibody Collaboration, at December 31, 2014 and 2013, amounts receivable from Sanofi totaled $110.6 million and $106.1 million and deferred revenue was $64.4 million and $71.2 million, respectively.
	b. Bayer HealthCare LLC
	The Company and Bayer HealthCare globally collaborate on the development and commercialization of EYLEA outside of the United States. The Company and Bayer HealthCare share the costs of the development of EYLEA. Bayer HealthCare commenced sales of EYLEA for the treatment of wet AMD in the fourth quarter of 2012, for the treatment of macular edema secondary to CRVO in the fourth quarter of 2013, and for the treatment of DME in the third quarter of 2014 following receipt of regulatory approvals outside the United States. In addition, Bayer HealthCare commenced sales of EYLEA for the treatment of mCNV in the fourth quarter of 2014. Bayer HealthCare markets EYLEA outside the United States, where, for countries other than Japan, the Company and Bayer HealthCare will share equally in profits and losses from sales of EYLEA. The Company is entitled to receive a percentage of between 33.5% and 40.0% of EYLEA annual sales in Japan. Within the United States, the Company is responsible for commercialization of EYLEA and retains exclusive rights to all profits from such commercialization in the United States.
	In January 2014, the Company entered into a license and collaboration agreement with Bayer HealthCare governing the joint development and commercialization outside the United States of an antibody product candidate to Platelet Derived Growth Factor Receptor Beta (PDGFR-beta).
	The collaboration revenue the Company earned from Bayer HealthCare is detailed below:
		Year Ended December 31,
	Bayer HealthCare Collaboration Revenue	2014			2013			2012
	EYLEA:
	Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	301,302		$	101,494		—
	Sales and substantive development milestones	105,000			70,000			$	25,000
	Cost-sharing of Regeneron EYLEA development expenses	23,383			20,905			34,892
	Other	52,390			27,890			10,207
	Total EYLEA	482,075			220,289			70,099
	PDGFR-beta antibody:
	Cost-sharing of REGN2176-3 development expenses	2,848			—			—
	Other	10,632			—			—
	Total PDGFR-beta	13,480			—			—
		$	495,555		$	220,289		$	70,099
	EYLEA outside the United States
	In October 2006, the Company entered into a license and collaboration agreement with Bayer HealthCare for the global development and commercialization outside the United States of EYLEA. Under the terms of the agreement, Bayer HealthCare made a non-refundable up-front payment to the Company of $75.0 million. The Company also received from Bayer HealthCare a $20.0 million development milestone payment in 2007 (which, for the purpose of revenue recognition, was not considered substantive).
	Since 2009, all agreed upon EYLEA development expenses incurred by the Company and Bayer HealthCare, under a global development plan, are being shared equally. The Company is also obligated to use commercially reasonable efforts to supply clinical and commercial bulk product of EYLEA. Bayer HealthCare has the right to terminate the license and collaboration agreement without cause with at least six months or twelve months advance notice depending on defined circumstances at the time of termination. In the event of termination of the agreement for any reason, the Company retains all rights to EYLEA.
	The Company is obligated to reimburse Bayer HealthCare out of its share of the collaboration profits (including the Company's percentage of sales of EYLEA in Japan) for 50% of the agreed upon development expenses that Bayer HealthCare has incurred in accordance with a formula based on the amount of development expenses that Bayer HealthCare has incurred and the Company's share of the collaboration profits, or at a faster rate at the Company's option. The Company's contingent reimbursement obligation to Bayer HealthCare was approximately $263 million as of December 31, 2014.
	In 2012, the Company earned and received a $15.0 million and $10.0 million substantive milestone payment related to marketing and pricing approval, respectively, of EYLEA for the treatment of wet AMD in Japan. In 2013, the Company earned and received a $15.0 million and a $10.0 million substantive milestone payment related to marketing and pricing approval, respectively, of EYLEA for the treatment of macular edema secondary to CRVO. In addition, in 2013, the Company earned and recorded as revenue, three $15.0 million sales milestone payments from Bayer HealthCare upon total aggregate net sales of EYLEA outside the United States exceeding $200 million, $300 million, and $400 million, respectively, over a twelve-month period. During 2014, the Company earned, and recorded as revenue, six $15.0 million sales milestones from Bayer HealthCare upon total aggregate net sales of EYLEA outside the United States exceeding $500 million, $600 million, $700 million, $800 million, $900 million, and $1.0 billion, respectively, over a twelve-month period. In addition, in connection with a November 2013 agreement under which Bayer HealthCare obtained rights to use certain of the Company's EYLEA clinical data for a regulatory filing, the Company earned, and recorded as revenue, a $15.0 million sales milestone from Bayer HealthCare upon total aggregate net sales of specific commercial supplies of EYLEA outside the United States exceeding $100 million over a twelve-month period. The Company is eligible to receive one additional $15.0 million sales milestone payment if twelve-month sales of specific commercial supplies of EYLEA outside the United States exceed $200 million.
	In January 2014, Bayer HealthCare decided to participate in the global development and commercialization of EYLEA outside the United States for the treatment of macular edema following BRVO. In connection with this decision, Bayer HealthCare reimbursed Regeneron $15.7 million for a defined share of the EYLEA global development costs that the Company had incurred prior to February 2014 for the BRVO indication, which was recognized as Bayer HealthCare collaboration revenue in 2014 and is included with "Cost-sharing of Regeneron EYLEA development expenses" for the year ended December 31, 2014 in the table above. In addition, all future agreed upon global EYLEA development expenses incurred in connection with BRVO are being shared equally, and any future profits or losses on sales of EYLEA outside of the United States for the treatment of macular edema following BRVO will also be shared (for countries other than Japan). The Company is entitled to receive a tiered percentage of EYLEA net sales in Japan.
The $75.0 million up-front licensing payment and the $20.0 million milestone payment received in 2007 from Bayer HealthCare are being recognized as collaboration revenue over the related estimated performance period in accordance with the Company's revenue recognition policy as described in Note 2. In periods when the Company recognizes EYLEA development expenses that the Company incurs under the collaboration, the Company also recognizes, as collaboration revenue, the portion of those EYLEA development expenses that is reimbursable from Bayer HealthCare. In periods when Bayer HealthCare incurs agreed upon EYLEA development expenses that benefit the collaboration and Regeneron, the Company also recognizes, as additional research and development expense, the portion of Bayer HealthCare's EYLEA development expenses that the Company is obligated to reimburse. In 2014, 2013, and 2012, the Company recognized as additional research and development expense $18.6 million, $15.3 million, and $21.9 million, respectively, of EYLEA development expenses that the Company was obligated to reimburse to Bayer HealthCare.
In connection with the companies' EYLEA collaboration, $155.8 million and $63.2 million was receivable from Bayer HealthCare at December 31, 2014 and 2013, respectively. In addition, at December 31, 2014 and 2013, deferred revenue from the Company's EYLEA collaboration with Bayer HealthCare was $60.2 million and $36.4 million, respectively.
PDGFR-beta antibody outside the United States
In January 2014, the Company entered into an agreement with Bayer HealthCare governing the joint development and commercialization outside the United States of an antibody product candidate to PDGFR-beta, including in combination with EYLEA, for the treatment of ocular diseases or disorders. REGN2176-3, a combination product candidate comprised of an antibody to PDGFR-beta co-formulated with EYLEA, is being developed under the agreement. Under the agreement, the Company will conduct the initial development of the PDGFR-beta antibody through completion of the first proof-of-concept study, upon which Bayer HealthCare will have a right to opt-in to license and collaborate on further development and commercialization outside the United States.
In connection with the agreement, Bayer HealthCare made a $25.5 million non-refundable upfront payment to the Company in January 2014, and is obligated to pay 25% of global development costs and 50% of development costs exclusively for the territory outside the United States under the initial development plan. In addition, Bayer HealthCare is obligated to reimburse the Company for 50% of development milestone payments to Sanofi related to the Company's acquisition of rights to antibodies targeting the PDGF family of receptors in May 2013, as described above. In that regard, Bayer HealthCare made two $2.5 million development milestone payments to the Company in 2014 (both of which, for the purpose of revenue recognition, were not considered substantive). Further, in connection with the Company's initial development of the PDGFR-beta antibody through completion of the first proof-of-concept study, the Company is eligible to receive up to $15.0 million in future development milestone payments from Bayer HealthCare, although certain of these development milestone payments could be reduced by half if Bayer HealthCare does not opt-in to the collaboration.
From inception of the agreement until Bayer HealthCare has the right to opt-in to the collaboration, the Company's sole significant deliverable is research and development services provided in accordance with the agreement. Therefore, the $25.5 million upfront payment was allocated to this deliverable, initially recorded as deferred revenue, and will be recognized as revenue over the related performance period. In addition, the two $2.5 million non-substantive development milestone payments from Bayer HealthCare were also initially recorded as deferred revenue and will be recognized over the same performance period as the upfront payment.
If Bayer HealthCare exercises its right to opt-in to the collaboration, it will obtain exclusive commercialization rights to the product outside the United States, continue to pay for 25% of global development costs and 50% of development costs exclusively for the territory outside the United States, pay a $20.0 million opt-in payment to the Company, pay a $20.0 million development milestone to the Company upon receipt of the first marketing approval in the European Union or Japan, share profits and losses from sales outside the United States equally with the Company, and be responsible for the payment of royalties on sales outside the United States to Sanofi.
Within the United States, the Company has exclusive commercialization rights and will retain all of the profits from sales. If Bayer HealthCare does not opt-in to the collaboration, the Company will have exclusive rights to develop and commercialize PDGFR-beta antibodies (except as a combination product with EYLEA) for use outside the United States.
The Company also has the right to opt-out of the collaboration upon completion of the first proof-of-concept study for the PDGFR-beta antibody. If the Company opts-out of the collaboration and Bayer HealthCare exercises its right to opt-in to the collaboration, Bayer HealthCare will obtain exclusive rights to the PDGFR-beta antibody (except as a combination product with EYLEA) outside of the United States, be responsible for all development costs outside of the United States, be responsible for all royalty and milestone payments to a third party, and will retain all of the profits from sales of the PDGFR-beta antibody outside of the United States.
Under the agreement, Bayer HealthCare has also agreed to a "standstill" provision, which prohibits Bayer HealthCare and its affiliates from seeking to influence the control of the Company or acquiring more than 20% of the Company's then outstanding shares of Class A Stock and Common Stock (taken together).
Unless terminated earlier in accordance with its provisions, the agreement will continue to be in effect until such time as neither party or its respective affiliates or sublicensees is developing or commercializing a PDGFR-beta antibody in the specified field outside of the United States and such discontinuation is acknowledged as permanent by both the Company and Bayer HealthCare in writing.
In connection with the companies' PDGFR-beta collaboration, $1.2 million was receivable from Bayer HealthCare at December 31, 2014. In addition, at December 31, 2014, deferred revenue from the Company's PDGFR-beta collaboration with Bayer HealthCare was $19.9 million.
c. Avalanche Biotechnologies, Inc.
In May 2014, the Company entered into a research collaboration and license agreement with Avalanche Biotechnologies, Inc. to discover, develop, and commercialize novel gene therapy products for the treatment of ophthalmologic diseases. In connection with the agreement, the Company made a $2.0 million upfront payment and a $6.0 million pre-payment of collaboration research costs, and is obligated to pay potential additional research costs, an aggregate amount of up to $80.0 million per product upon meeting certain potential development and regulatory milestones (for products directed to as many as eight therapeutic targets, or up to an aggregate of $640.0 million), and royalties on any future sales of such products. The Company also purchased an aggregate of $5.0 million of Avalanche preferred stock. Under the agreement, the Company collaborates with Avalanche to conduct research for the discovery of novel gene therapy vectors. Subsequent to the filing of an Investigational New Drug application ("IND") with the FDA for a product candidate developed under the agreement, Regeneron may exercise its right to obtain exclusive worldwide rights to further research, develop, and commercialize such product candidates directed to the applicable therapeutic target. In addition, Avalanche has the option to share in development costs and profits for products directed toward up to two therapeutic targets of its choice.
In July 2014, Avalanche commenced an initial public offering ("IPO") of its common stock and thereby triggered the Company's obligation under the research collaboration and license agreement to purchase up to $10.0 million of Avalanche common stock in a concurrent private placement. As part of the concurrent private placement, the Company purchased from Avalanche at the closing of the IPO 588,235 shares of Avalanche common stock for an aggregate purchase price of $10.0 million. In addition, at the closing of the IPO, Avalanche preferred stock, including the Avalanche preferred stock held by the Company, automatically converted on a one-for-one basis into Avalanche common stock.
d. Other
In addition to the collaboration agreements discussed above, the Company has various other collaboration agreements that are not individually, or in the aggregate, significant to its operating results or financial condition at this time. Pursuant to the terms of those agreements, the Company may be required to pay, or it may receive, additional amounts upon the achievement of various development and commercial milestones which in the aggregate could be significant. The Company may also incur, or get reimbursed for, significant research and development costs if the related product candidate(s) were to advance to late stage clinical trials. In addition, if any products related to these collaborations are approved for sale, the Company may be required to pay, or it may receive, royalties on future sales. The payment or receipt of these amounts, however, is contingent upon the occurrence of various future events.

Technology_Licensing_Agreement

Technology Licensing Agreements	12 Months Ended
	Dec. 31, 2014
Technology Licensing Agreements [Abstract]
Technology Licensing Agreements	Technology Licensing Agreement
	In March 2007, the Company entered into a six-year, non-exclusive license agreement with Astellas Pharma Inc. to allow Astellas to utilize the Company's VelocImmune technology in its internal research programs to discover human monoclonal antibodies. In July 2010, the license agreement with Astellas was amended and extended through June 2023. Under the terms of the amended agreement, Astellas made a $165.0 million up-front payment to the Company in August 2010, which was deferred upon receipt and is being recognized as revenue ratably over the seven-year period beginning in mid-2011. In addition, Astellas will make a $130.0 million second payment to the Company in June 2018 unless the license agreement has been terminated prior to that date. Astellas has the right to terminate the agreement at any time by providing 90 days' advance written notice. Under certain limited circumstances, such as a material breach of the agreement by the Company, Astellas may terminate the agreement and receive a refund of a portion of its up-front payment or, if such termination occurs after June 2018, a portion of its second payment, to the Company under the July 2010 amendment to the agreement. The Company is entitled to receive a mid-single digit royalty on any future sales of antibody products discovered by Astellas using the Company's VelocImmune technology. In connection with the Astellas license agreement, for each of the years ended December 31, 2014, 2013, and 2012, the Company recognized $23.6 million of technology licensing revenue. In addition, deferred revenue at December 31, 2014 and 2013 was $81.0 million and $104.6 million, respectively.

Marketable_Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities
	Marketable securities as of December 31, 2014 and December 31, 2013 consist of both debt securities issued by investment grade institutions as well as equity securities. The Company also held restricted marketable securities as of December 31, 2014, consisting of the Company's investment in Avalanche common shares (see Note 4), which were subject to customary transfer restrictions until January 2015 under a lock-up agreement with the underwriters of Avalanche's IPO.
	The following tables summarize the Company's investments in marketable securities:
			Amortized			Unrealized						Fair
	As of December 31, 2014		Cost Basis			Gains			Losses			Value
	Unrestricted
	Corporate bonds		$	548,832		$	136		$	(1,462	)	$	547,506
	U.S. government and government agency obligations		28,596			3			(46		)	28,553
	Municipal bonds		37,044			37			(43		)	37,038
	Equity securities		2,005			5,374			—			7,379
			616,477			5,550			(1,551		)	620,476
	Restricted
	Equity securities		15,000			76,439			—			91,439
			$	631,477		$	81,989		$	(1,551	)	$	711,915
	As of December 31, 2013
	Unrestricted
	Corporate bonds		$	369,321		$	233		$	(361	)	$	369,193
	U.S. government and government agency obligations		107,493			55			(27		)	107,521
	Commercial paper		23,891			53			—			23,944
	Municipal bonds		36,935			45			(59		)	36,921
	International government agency obligations		2,007			1			—			2,008
	Certificates of deposit		7,509			5			—			7,514
	Equity securities		1,166			—			—			1,166
			$	548,322		$	392		$	(447	)	$	548,267
	The Company classifies its debt security investments based on their contractual maturity dates. The debt securities listed as of December 31, 2014 mature at various dates through August 2024. The fair values of debt security investments by contractual maturity consist of the following:
			As of December 31,
			2014			2013
	Maturities within one year		$	251,761		$	158,376
	Maturities after one year through five years		360,208			383,410
	Maturities after five years through ten years		1,128			4,138
	Maturities after ten years		—			1,177
			$	613,097		$	547,101
	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 December 31, 2014	Fair Value			Unrealized Loss			Fair Value			Unrealized Loss		Fair Value		Unrealized Loss
	Corporate bonds	$	390,613		$	(1,462	)	—			—		$	390,613	$	(1,462	)
	U.S. government and government agency obligations	25,549			(46		)	—			—		25,549		(46		)
	Municipal bonds	10,779			(43		)	—			—		10,779		(43		)
		$	426,941		$	(1,551	)	—			—		$	426,941	$	(1,551	)
	As of December 31, 2013
	Corporate bonds	$	176,140		$	(361	)	—			—		$	176,140	$	(361	)
	U.S. government and government agency obligations	49,241			(27		)	—			—		49,241		(27		)
	Municipal bonds	14,431			(59		)	—			—		14,431		(59		)
		$	239,812		$	(447	)	—			—		$	239,812	$	(447	)
	During the year ended December 31, 2013, the Company recorded an other-than-temporary impairment charge of $2.9 million related to its investment in an equity security. There were no other-than-temporary impairment charges recorded on the Company's investments during 2014 or 2012.
	Realized gains and losses are included as a component of investment income. For the year ended December 31, 2014, total realized gains on sales of marketable securities were $1.2 million, and there were no realized losses. For the year ended December 31, 2013, total realized gains on sales of marketable securities were $1.0 million, and there were no realized losses. For the year ended December 31, 2012, total realized gains and losses on sales of marketable securities were not material.
	Changes in the Company's accumulated other comprehensive income (loss) for the years ended December 31, 2014, 2013, and 2012 related to unrealized gains and losses on available-for-sale marketable securities. For the years ended December 31, 2014 2013, and 2012, amounts reclassified from accumulated other comprehensive income (loss) into investment income in the Company's Statements of Operations were related to the impairment charge on the equity security and realized gains and losses on sales of marketable securities described above.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 December 31, 2014	Fair Value		Quoted Prices in		Significant Other
				Active Markets		Observable Inputs
				for Identical		(Level 2)
				Assets
				(Level 1)
	Available-for-sale marketable securities:
	Unrestricted
	Corporate bonds	$	547,506	—		$	547,506
	U.S. government and government agency obligations	28,553		—		28,553
	Municipal bonds	37,038		—		37,038
	Equity securities	7,379		$	7,379	—
		620,476		7,379		613,097
	Restricted
	Equity securities	91,439		—		91,439
		$	711,915	$	7,379	$	704,536
	As of December 31, 2013
	Available-for-sale marketable securities:
	Unrestricted
	Corporate bonds	$	369,193	—		$	369,193
	U.S. government and government agency obligations	107,521		—		107,521
	Commercial paper	23,944		—		23,944
	Municipal bonds	36,921		—		36,921
	International government agency obligations	2,008		—		2,008
	Certificates of deposit	7,514		—		7,514
	Equity securities	1,166		$	1,166	—
		$	548,267	$	1,166	$	547,101
	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 in 2014, 2013, and 2012.
	During 2013, the Company sold one Level 3 marketable security and realized a gain on its sale which was not material. There were no purchases or maturities of Level 3 marketable securities and no unrealized gains or losses related to Level 3 marketable securities for the years ended December 31, 2014 and 2013. There were no transfers of marketable securities between Levels 1, 2, or 3 classifications during the years ended December 31, 2014 and 2013.
	As of December 31, 2014 and 2013, the Company had $169.4 million and $400.0 million, respectively, in aggregate principal amount of 1.875% convertible senior notes (the "Notes") that will mature on October 1, 2016 unless earlier converted or repurchased. As described in Note 12, a portion of the Notes was surrendered for conversion during 2014. The fair value of the outstanding Notes was estimated to be $819.8 million and $1,327.2 million as of December 31, 2014 and 2013, respectively, and was determined based on Level 2 inputs, such as market and observable sources.
	Additionally, as described in Note 12, a portion of the Company's warrants are classified as a liability and measured at fair value as of December 31, 2014. The fair value of this liability was estimated to be $87.5 million as of December 31, 2014, and was determined based on Level 2 inputs, such as market and observable sources.

Inventory

Inventory	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Inventory	Inventories
	Inventories consist of the following:
		As of December 31,
		2014		2013
	Raw materials	$	10,923	$	9,120
	Work-in-process	73,519		35,868
	Finished goods	10,768		14,352
	Deferred costs	33,651		11,014
		$	128,861	$	70,354
	Deferred costs represent the costs of product manufactured and shipped to the Company's collaborators for which recognition of revenue has been deferred (see Note 2). In 2014, 2013, and 2012, cost of goods sold included inventory write-downs and reserves totaling $6.0 million, $9.1 million, and $17.0 million, respectively.

Property_Plant_and_Equipment

Property, Plant, and Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant, and Equipment
	Property, plant, and equipment consist of the following:
		As of December 31,
		2014			2013
	Land	$	2,768		$	2,768
	Building and improvements	398,981			343,363
	Leasehold improvements	42,600			26,370
	Construction-in-progress	472,231			142,370
	Laboratory and other equipment	253,058			189,543
	Furniture, computer and office equipment, and other	58,655			44,186
		1,228,293			748,600
	Less, accumulated depreciation and amortization	(253,984		)	(221,617		)
		$	974,309		$	526,983
	As of December 31, 2014, $219.6 million of the Company’s property, plant, and equipment was located in Ireland and $754.7 million was located in the United States. As of December 31, 2013, $23.5 million of the Company’s property, plant, and equipment was located in Ireland and $503.5 million was located in the United States.
	Depreciation and amortization expense on property, plant, and equipment amounted to $52.7 million, $41.2 million, and $36.9 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	Property, plant, and equipment, at cost, as of December 31, 2014 and 2013 included $236.7 million and $111.1 million, respectively, of costs incurred by the Company's landlord to construct laboratory and office facilities in Tarrytown, New York. See Note 13a.

Accounts_Payable_and_Accrued_E

Accounts Payable and Accrued Expenses	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Accounts Payable and Accrued Expenses	Accounts Payable and Accrued Expenses
	Accounts payable and accrued expenses consist of the following:
		As of December 31,
		2014		2013
	Accounts payable	$	99,508	$	61,936
	Accrued payroll and related costs	92,778		69,429
	Accrued clinical trial expense	41,555		23,654
	Accrued sales-related charges, deductions, and royalties	133,085		66,855
	Other accrued expenses and liabilities	117,302		29,022
		$	484,228	$	250,896
	Included within "other accrued expenses and liabilities" as of December 31, 2014 is $59.8 million payable to a warrant holder in February 2015 in connection with an agreement to reduce a portion of the number of warrants held. See Note 12.

Deferred_Revenue

Deferred Revenue	12 Months Ended
	Dec. 31, 2014
Deferred Revenue Disclosure [Abstract]
Deferred Revenue	Deferred Revenue
	Deferred revenue consists of the following:
		As of December 31,
		2014		2013
	Current portion:
	Received or receivable from Sanofi (see Note 4a)	$	15,927	$	12,815
	Received or receivable from Bayer HealthCare (see Note 4b)	33,652		9,738
	Received for technology license agreement (see Note 5)	23,572		23,572
	Other	874		875
		$	74,025	$	47,000
	Long-term portion:
	Received or receivable from Sanofi (see Note 4a)	$	72,367	$	76,522
	Received or receivable from Bayer HealthCare (see Note 4b)	46,486		26,683
	Received for technology license agreement (see Note 5)	57,423		80,994
		$	176,276	$	184,199

Convertible_Debt

Convertible Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Convertible Debt	Convertible Debt
	In October 2011, the Company issued $400.0 million aggregate principal amount of 1.875% convertible senior notes (the "Notes") in a private placement.
	The Notes pay interest semi-annually on April 1 and October 1, which began April 1, 2012, and will mature on October 1, 2016 unless earlier converted or repurchased. The Notes are convertible, subject to certain conditions, into cash, shares of the Company's Common Stock, or a combination of cash and shares of Common Stock, at the Company's option. The initial conversion rate for the Notes is 11.9021 shares of Common Stock (subject to adjustment in certain circumstances) per $1,000 principal amount of the Notes, or a total of approximately 4,760,840 shares upon conversion, which is equal to an initial conversion price of approximately $84.02 per share. A holder of the Notes may surrender its Notes at its option any time prior to the close of business on the business day immediately preceding July 1, 2016, only under the following circumstances: (i) during any calendar quarter commencing after the calendar quarter ending on December 31, 2011 (and only during such calendar quarter), if the last reported sale price of the Company's Common Stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (ii) during the five business day period after any ten consecutive trading day period (the "measurement period") in which the trading price, as defined, of the Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company's Common Stock and the conversion rate on each such trading day; (iii) if the Company elects to issue to all or substantially all holders of its Common Stock any rights, options or warrants (other than pursuant to a rights plan) entitling them for a period of not more than 60 calendar days after the record date for such issuance, to subscribe for or purchase shares of the Company's Common Stock, at a price per share less than the average of the last reported sales prices of the Company's Common Stock for the ten consecutive day period ending on, and including, the trading day immediately preceding the declaration date for such issuance; (iv) upon specified distributions to the Company's shareholders; or (v) upon the occurrence of specified corporate transactions, such as a fundamental change (i.e., a change in control), or the Company's Common Stock ceasing to be listed on at least one U.S. national securities exchange. On or after July 1, 2016, holders may convert their Notes at the conversion rate at any time prior to the close of business on the second scheduled trading day immediately preceding the maturity date irrespective of the foregoing conditions. In the event that a fundamental change, as defined in the indenture under which the Notes have been issued, occurs prior to maturity of the Notes, the initial conversion rate may be increased to include additional shares upon conversion, or holders can require the Company to purchase from them all or a portion of their Notes for 100% of the principal value plus any accrued and unpaid interest.
	The Company has reserved sufficient shares of its Common Stock to satisfy the conversion requirements related to the Notes. The Company may not redeem the Notes prior to their maturity date.
	As of December 31, 2014, the "if converted value" exceeded the principal amount of the Notes by $691.6 million.
	In accordance with accounting guidance for debt with conversion and other options, the Company accounted for the liability and equity components of the Notes separately. The estimated fair value of the liability component at the date of issuance was $271.1 million, and was computed based on the fair value of similar debt instruments that do not include a conversion feature. The equity component of $120.9 million was recognized as a debt discount and represents the difference between the $392.0 million of gross proceeds from the issuance of the Notes and the $271.1 million estimated fair value of the liability component at the date of issuance. The debt discount is amortized over the expected life of a similar liability without the equity component. The Company determined this expected life to be equal to the term of the Notes, resulting in an amortization period ending October 1, 2016. The effective interest rate used to amortize the debt discount is approximately 10.2%, which was based on the Company's estimated non-convertible borrowing rate as of the date the Notes were issued.
	In connection with the offering of the Notes in October 2011, the Company entered into convertible note hedge ("call option") and warrant transactions with multiple counterparties, including an affiliate of the initial purchaser of the Notes. The convertible note hedge transactions cover, subject to customary anti-dilution adjustments, the number of shares of the Company's Common Stock that initially underlie the Notes, and are intended to reduce the potential dilutive impact of the conversion feature of the Notes. The convertible note hedge will terminate upon the earlier of the maturity date of the Notes or the first day the Notes are no longer outstanding. The Company paid $117.5 million for the convertible note hedge, which was recorded as a reduction to additional paid-in capital. The warrant transactions have an initial strike price of approximately $103.41 per share, and may be settled in cash or shares of the Company's Common Stock, at the Company's option. The warrant transactions have a dilutive effect to the extent that the market price per share of the Company's Common Stock exceeds the applicable strike price of the warrants. Proceeds received from the warrant transactions totaled $93.8 million and were recorded as additional paid-in capital. The warrants will become exercisable (and, if not exercised, will expire) at various dates during 2017. The original convertible note hedge and warrants were both considered indexed to the Company's Common Stock and classified as equity; therefore, the convertible note hedge and warrants were not accounted for as derivative instruments. The Company has reserved sufficient shares of its Common Stock to satisfy the potential settlement of the warrants.
	During 2014, $230.6 million principal amount of the Company's $400.0 million aggregate principal amount of Notes was surrendered for conversion, of which $220.6 million was settled prior to December 31, 2014. In accordance with the terms of the Notes, the Company elected to settle these conversion obligations through a combination of cash, in an amount equal to the principal amount of the converted Notes, and shares of the Company's Common Stock in respect of any amounts due in excess thereof. Consequently, in connection with the Note conversions during 2014, the Company (i) paid $220.6 million in cash, (ii) issued 2,017,732 shares of Common Stock, (iii) recognized a $33.5 million loss on the debt extinguishment, and (iv) allocated $691.9 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 stockholder's equity. Settlement on the remaining portion of Notes surrendered during 2014 is anticipated during Q1 2015.
	In addition to the Note conversions described above, the Company received notification in the first quarter of 2015 that an additional $6.7 million principal amount of the Notes were surrendered for conversion, and settlement is anticipated during the first quarter of 2015. The Company has elected to settle all conversion obligations for which it has been given notice (which have not yet settled) through a combination of cash and shares (total payment will be based on the average of the volume-weighted-average prices of the Common Stock during the 40 trading-day cash settlement averaging period specified in the indenture governing the Notes). In connection with these Note conversions, the Company exercised a proportionate amount of its convertible note hedges, for which the Company expects to receive shares of Common Stock equivalent to the number of shares the Company will be required to issue to settle the non-cash portion of the related Note conversions.
	The net carrying amount of the liability component of the Notes consists of the following:
		As of December 31,
		2014			2013
	Total convertible senior notes - par	$	169,400		$	400,000
	Unamortized discount	(22,627		)	(79,685		)
		$	146,773		$	320,315
	Total interest expense associated with the Notes, net of capitalized interest as applicable (see Note 21), consists of the following:
		Year Ended December 31,
		2014			2013			2012
	Contractual coupon interest rate	$	5,036		$	7,230		$	7,503
	Amortization of discount and note issuance costs	17,821			22,980			21,623
		$	22,857		$	30,210		$	29,126
	As a result of the 2014 Note conversions described above, the Company also exercised a proportionate amount of its convertible note hedges during 2014, for which the Company received 2,017,732 shares of Common Stock, which was equivalent to the number of shares the Company was required to issue to settle the non-cash portion of the related Note conversions. The shares received were recorded as Treasury Stock, at cost, in the Company's Balance Sheet and Statement of Stockholders' Equity.
	Also during 2014, the Company entered into agreements to reduce the number of warrants held by the warrant holders. Pursuant to the agreements, the Company paid an aggregate amount of $294.6 million to the warrant holders to reduce the maximum number of shares of Common Stock issuable upon exercise of the warrants from 4,760,840 to 3,540,095 (subject to adjustment from time to time as provided in the applicable warrant agreements).
	Additionally in November 2014, the Company entered into an amendment agreement with a warrant holder whereby the parties have agreed to reduce a portion of the number of warrants held by the warrant holder by up to a maximum of 493,229, for an aggregate amount payable by the Company not to exceed $148.5 million. The reduction in the number of warrants will be determined based on the number of warrants with respect to which the warrant holder has closed out its hedge position, provided that the warrant holder does not effect any purchases at a price per share exceeding $397.75 per share, during the period starting on November 26, 2014 and ending no later than February 12, 2015. The Company is obligated to settle any payments due under the amendment agreement in February 2015. Given that the amendment agreement contains a conditional obligation that requires settlement in cash, and the Company's obligation is indexed to the Company's share price, the Company reclassified the estimated fair value of the 493,229 warrants from additional paid-in capital to a liability in November 2014, with such liability subsequently measured at fair value with changes in fair value recognized in earnings. The change in fair value for the year ended December 31, 2014 resulted in the Company recording a gain of $1.2 million.
	As a result of the warrant holder closing out a portion of its hedge position prior to December 31, 2014, the Company recorded a $59.8 million accrued liability in connection with the warrant holder reducing the number of warrants it held by 202,560 as of December 31, 2014. The estimated fair value of the remaining liability as of December 31, 2014 is $87.5 million, and is recorded within other current liabilities within the Company's Balance Sheet. During the first quarter of 2015, the warrant holder closed out additional portions of its hedge position, and, as a result, the Company expects to pay an additional $62.0 million to further reduce the number of warrants held by such warrant holder by 206,480. At the expiration of the November 2014 amended agreement, any remaining warrants will be re-measured at fair value and reclassified back to additional paid-in capital, consistent with the original classification of the warrants under the 2011 issuance.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies
	a. Leases
	Descriptions of Lease Agreements
	The Company leases laboratory and office facilities in Tarrytown, New York. The facilities leased by the Company in Tarrytown include (i) space in previously existing buildings, (ii) newly constructed space in two buildings ("Buildings A and B") that was completed in the third quarter of 2009 and, (iii) under a December 2009 amendment to the lease, additional newly constructed space in a third building ("Building C") that was completed in the first quarter of 2011. The lease agreement related to Buildings A, B, and C will expire in June 2029; the remaining facilities under lease will expire in June 2024. The Tarrytown lease contains three renewal options to extend the term of the lease by five years each, escalations at 2.5% per annum, and early termination options for various portions of the space. The lease provides for monthly payments over its term and additional charges for utilities, taxes, and operating expenses.
	In April 2013, the Company entered into a lease agreement for additional laboratory and office space to be constructed in two new buildings ("Buildings D and E"), which are expected to be completed in the second half of 2015, at the Company's current Tarrytown, New York location. The initial term of the lease, which commenced during the second half of 2014, is approximately 15 years and contains three renewal options to extend the term of the lease by five years each. The lease provides for (i) monthly payments over its term, which will be based on the landlord's costs of construction and tenant allowances, and (ii) additional charges for utilities, taxes, and operating expenses.
	Certain premises under the Tarrytown lease are accounted for as operating leases. However, as described further below under "Facility Lease Obligations," for Buildings A, B, C, D, and E (collectively, the "Buildings") that the Company is leasing, the Company is deemed, in substance, to be the owner of the landlord's Buildings in accordance with the application of FASB authoritative guidance.
	The Company also leases certain other laboratory, office, and storage space and equipment under operating leases which expire at various times through 2022.
	Commitments under Operating Leases
	The estimated future minimum noncancelable lease commitments under operating leases, as of December 31, 2014, are as follows:
		Facilities		Equipment		Total
	2015	$	9,370	$	1,449	$	10,819
	2016	10,040		151		10,191
	2017	9,592		13		9,605
	2018	9,779		—		9,779
	2019	9,957		—		9,957
	Thereafter	58,271		—		58,271
		$	107,009	$	1,613	$	108,622
	Rent expense under operating leases was:
	Year Ended December 31,	Facilities		Equipment		Total
	2014	$	13,360	$	952	$	14,312
	2013	9,404		471		9,875
	2012	7,428		601		8,029
	In addition to its rent expense under operating leases, and payments under facility lease obligations (see below), for various facilities, the Company paid rental charges for utilities, real estate taxes, and operating expenses of $13.6 million, $11.5 million, and $10.9 million for the years ended December 31, 2014, 2013, and 2012, respectively.
	Facility Lease Obligations
	Based upon various factors, including the Company's involvement in the construction of the Buildings and its responsibility for directly paying for a substantial portion of tenant improvements, the Company is deemed, in substance, to be the owner of the landlord's Buildings in accordance with the application of FASB authoritative guidance. Consequently, in addition to capitalizing the tenant improvements, the Company capitalizes the landlord's costs of constructing these new facilities, offset by a corresponding lease obligation on the Company's Balance Sheet. The Company also recognizes, as additional facility lease obligation, reimbursements from the Company's landlord for tenant improvement costs that the Company incurred since such payments that the Company receives from its landlord are deemed to be a financing obligation. The Company allocates a portion of its lease payments on these facilities between the Buildings and the land on which the Buildings are constructed, based on the initial estimated relative fair values of the land and Buildings. The land element of the lease is treated for accounting purposes as an operating lease.
	With respect to Buildings A and B, in 2009 monthly lease payments commenced and the buildings were placed in service by the Company. The imputed interest rate applicable to the Company's Buildings A and B facility lease obligation is approximately 11%. With respect to Building C, in 2011, monthly lease payments commenced and the building was placed in service by the Company. The imputed interest rate applicable to the Company's Building C facility lease obligation is approximately 9%. In 2014, 2013, and 2012, the Company recognized $14.5 million, $16.2 million, and $16.0 million, respectively, of interest expense in connection with the Buildings A and B and the Building C facility lease obligations. As of December 31, 2014 and 2013, the Buildings A and B facility lease obligation balance was $110.2 million and $111.2 million, respectively, and the Building C facility lease obligation balance was $49.3 million and $49.1 million, respectively.
	The estimated future minimum noncancelable commitments under these facility lease obligations, as of December 31, 2014, are as follows:
		Buildings A and B		Building C		Total
	2015	$	13,545	$	4,562	$	18,107
	2016	13,809		4,688		18,497
	2017	14,079		4,818		18,897
	2018	14,356		4,951		19,307
	2019	14,640		5,088		19,728
	Thereafter	132,027		59,987		192,014
		$	202,456	$	84,094	$	286,550
	Commencing in the second quarter of 2013, the Company began capitalizing the landlord's costs of constructing Buildings D and E, and recognized a corresponding facility lease obligation. As of December 31, 2014 and 2013, the Buildings D and E facility lease obligation balance was $152.8 million and $25.0 million, respectively. Rent expense in connection with the land element of these new facilities also commenced in the second quarter of 2013 and is recorded as a deferred liability until lease payments commence, which is expected to be in 2015. Rent payments will be based on the landlord's costs of construction and tenant allowances, and will include additional charges for utilities, taxes, and operating expenses.
	b. Research Collaboration and Licensing Agreements
	As part of the Company's research and development efforts, the Company enters into research collaboration and licensing agreements with related and unrelated companies, scientific collaborators, and universities. These agreements contain varying terms and provisions which include fees to be paid by the Company, services to be provided, and ownership rights to certain proprietary technology developed under the agreements. Some of these agreements may require the Company to pay additional amounts upon the achievement of various development and commercial milestones, contingent upon the occurrence of various future events. Additionally, some of the agreements contain provisions which require the Company to pay royalties, as defined, at rates that range from 0.5% to 16.5%, in the event the Company sells or licenses any proprietary products developed under the respective agreements. The Company also has contingent reimbursement obligations to its collaborators Sanofi and Bayer HealthCare once the applicable collaboration becomes profitable. See Note 4 for additional information.
	In December 2011, the Company and Genentech, a member of the Roche Group, entered into a Non-Exclusive License and Partial Settlement Agreement (the "Original Genentech Agreement") that covered making, using, and selling EYLEA for the prevention of human eye diseases and disorders in the United States, and ended the litigation relating to those matters. Pursuant to the Original Genentech Agreement, the Company received a non-exclusive license to certain patents relating to VEGF receptor proteins, known as the Davis-Smyth patents, and other technology patents. The Original Genentech Agreement provided for the Company to make payments to Genentech based on U.S. sales of EYLEA commencing upon FDA approval of EYLEA in November 2011 through May 7, 2016. The Company made a one-time, non-refundable $60.0 million payment during 2012 upon cumulative U.S. sales of EYLEA reaching $400 million, and is obligated to pay royalties of 4.75% on cumulative U.S. sales of EYLEA between $400 million and $3 billion and 5.5% on any cumulative U.S sales of EYLEA over $3 billion. As the Company records net product sales of EYLEA, the Company is recognizing expense in connection with the Genentech Agreement using a blended mid-single digit royalty rate that reflects both the $60.0 million payment and the royalties payable on cumulative sales and that is based upon the Company's estimate of cumulative EYLEA sales through May 7, 2016.
	Effective May 17, 2013, the Company entered into an Amended and Restated Non-Exclusive License and Settlement Agreement with Genentech (the "Amended Genentech Agreement"), which amended the Original Genentech Agreement to now include all sales of EYLEA worldwide and ended the litigation relating to those matters. Under the Amended Genentech Agreement, the Company received a worldwide non-exclusive license to the Davis-Smyth patents, and certain other patents, owned or co-owned by Genentech for the prevention or treatment of eye diseases and eye disorders in a human through administration of EYLEA to the eye. Under the Amended Genentech Agreement, the Company is obligated to make payments to Genentech based on sales of EYLEA in the United States, and EYLEA manufactured in the United States and sold outside the United States, through May 7, 2016 using the same milestone and royalty rates as in the Original Genentech Agreement. EYLEA is sold outside the United States by affiliates of Bayer HealthCare under the Company's license and collaboration agreement. All payments to Genentech under the Original Genentech Agreement and the Amended Genentech Agreement have been or will be made by the Company. Bayer HealthCare will share in all such payments based on the proportion of ex-U.S. EYLEA sales to worldwide EYLEA sales and determined consistent with the license and collaboration agreement.
	The Company recognizes royalty expense based on product sales of commercial products under various licensing agreements, including, for EYLEA sales both inside and outside of the United States, the Genentech agreements described above. For the years ended December 31, 2014, 2013, and 2012, royalty expense related to product sales totaled $169.9 million, $128.1 million, and $59.5 million, respectively.

Stockholders_Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity
	The Company's Restated Certificate of Incorporation provides for the issuance of up to 40 million shares of Class A Stock, par value $0.001 per share, and 160 million shares of Common Stock, par value $0.001 per share. Shares of Class A Stock are convertible, at any time, at the option of the holder into shares of Common Stock on a share-for-share basis. Holders of Class A Stock have rights and privileges identical to Common Stockholders except that each share of Class A is entitled to ten votes per share, while each share of Common Stock is entitled to one vote per share. Class A Stock may only be transferred to specified Permitted Transferees, as defined. Under the Company's Restated Certificate of Incorporation, the Company's board of directors is authorized to issue up to 30 million shares of preferred stock, in series, with rights, privileges, and qualifications of each series determined by the board of directors.
	In December 2007, Sanofi purchased 12 million newly issued, unregistered shares of the Company's Common Stock for an aggregate cash price of $312.0 million. As a condition to the closing of this transaction, Sanofi entered into an investor agreement, as amended and restated in January 2014, with the Company. Under the terms of the amended and restated investor agreement, Sanofi has three demand rights to require the Company to use all reasonable efforts to conduct a registered underwritten public offering with respect to shares of the Company's Common Stock held by Sanofi from time to time. Under the amended and restated investor agreement, Sanofi has also agreed not to dispose of any shares of the Company's Common Stock beneficially owned by Sanofi from time to time until the later of (i) December 20, 2020, and (ii) the expiration of the Discovery Agreement with Sanofi, as amended (see Note 4a) if the agreement is extended beyond December 20, 2020. These restrictions on dispositions are subject to earlier termination upon the occurrence of certain events, such as the consummation of a change-of-control transaction involving the Company or the Company's dissolution or liquidation, and certain restrictions have been imposed on the manner of sales thereafter.
	Further, pursuant to the amended and restated investor agreement, Sanofi is bound by certain "standstill" provisions, which contractually prohibit Sanofi from seeking to directly or indirectly exert control of the Company or acquiring more than 30% of the outstanding shares of the Company's Class A Stock and Common Stock (taken together). This prohibition will remain in place until the earliest of (i) the later of the fifth anniversaries of the expiration or earlier termination of the Company's License and Collaboration Agreement with Sanofi and the Company's ZALTRAP Agreement with Sanofi, each as amended (see Note 4a) and (ii) other specified events. Sanofi has also agreed to vote as recommended by the Company's board of directors, except that it may elect to vote proportionally with the votes cast by all of the Company's other shareholders with respect to certain change-of-control transactions, and to vote in its sole discretion with respect to liquidation or dissolution, stock issuances equal to or exceeding 20% of the then outstanding shares or voting rights of the Company's Class A Stock and Common Stock (taken together), and new equity compensation plans or amendments if not materially consistent with the Company's historical equity compensation practices. The rights and restrictions under the investor agreement are subject to termination upon the occurrence of certain events.
	In addition, upon Sanofi reaching 20% ownership of the Company's then outstanding shares of Class A Stock and Common Stock (taken together) during 2014, the Company was required to appoint an individual agreed upon by the Company and Sanofi to the Company's board of directors. This individual is required to be independent of the Company, and not to be a current or former officer, director, employee, or paid consultant of Sanofi.
	In October 2011, the Company completed a private placement of $400.0 million aggregate principal amount of Notes, which are convertible into shares of the Company's Common Stock. In accordance with accounting guidance for debt with conversion and other options, the Company accounted for the liability and equity components of the Notes separately. The equity component of the Notes was $120.6 million, net of issuance costs. In connection with the offering of the Notes in October 2011, the Company entered into convertible note hedge and warrant transactions. The Company paid $117.5 million for the convertible note hedge, which was recorded as a reduction to additional paid-in capital. The warrant transactions have an initial strike price of approximately $103.41 per share, and may be settled in cash or shares of the Company's Common Stock, at the Company's option. Proceeds received from the warrant transactions totaled $93.8 million and were recorded as additional paid-in capital. The warrants will become exercisable (and, if not exercised, will expire) at various dates during 2017. See Note 12.
	During 2014, $220.6 million principal amount of the Company's Notes surrendered for conversion was settled as of December 31, 2014. A portion of the settlement consideration provided to the Note holders ($691.9 million) was allocated to the reacquisition of the equity component of the Notes. As a result of the Note conversions, the Company exercised a proportionate amount of its convertible note hedges, for which the Company received 2,017,732 shares of Common Stock. The shares received were recorded as Treasury Stock, at cost, in the Company's Balance Sheet and Statement of Stockholders' Equity.
	During 2014, the Company entered into agreements to reduce the number of warrants held by warrant holders. Pursuant to the agreements, the Company paid an aggregate amount of $294.6 million to the warrant holders to reduce the maximum number of shares of Common Stock issuable upon exercise of the warrants. In addition, in November 2014, the Company entered into an amendment agreement with a warrant holder whereby the parties have agreed to reduce a portion of the number of warrants held by the warrant holder by up to a maximum of 493,229, for an aggregate amount payable by the Company not to exceed $148.5 million. Given that the amendment agreement contains a conditional obligation that requires settlement in cash, and the Company's obligation is indexed to the Company's share price, the Company reclassified the estimated fair value of the warrants from additional paid-in capital to a liability in November 2014. See Note 12.
	In connection with the Company's January 2014 license and collaboration agreement with Bayer HealthCare for the joint development and commercialization outside the United States of antibody product candidates to PDGFR-beta (see Note 4b), Bayer HealthCare has also agreed to a "standstill" provision, which prohibits Bayer HealthCare and its affiliates from seeking to influence the control of the Company or acquiring more than 20% of the Company's then outstanding shares of Class A Stock and Common Stock (taken together).

LongTerm_Incentive_Plans

Long-Term Incentive Plans	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Long-Term Incentive Plans	Long-Term Incentive Plans
	During 2000, the Company established the Regeneron Pharmaceuticals, Inc. 2000 Long-Term Incentive Plan which, as amended and restated and approved by the Company's shareholders (the "2000 Incentive Plan"), provided for the issuance of up to 35,397,043 shares of Common Stock in respect of awards, in addition to any shares subject to awards that were returned to the 2000 Incentive Plan upon expiration, forfeiture, surrender, exchange, cancellation, or termination of previously granted awards.
	During 2014, the Company established, and the Company's shareholders approved, the Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan (the "2014 Incentive Plan"). As of the shareholder approval date, the 2014 Incentive Plan provides for the issuance of up to 16,485,333 shares of Common Stock in respect of awards (including 4,485,333 shares of Common Stock rolled over into the 2014 Incentive Plan from the 2000 Incentive Plan), in addition to any shares subject to awards under the 2000 Incentive Plan or the 2014 Incentive Plan that are added to the pool of shares available for grant under the 2014 Incentive Plan upon the expiration, forfeiture, surrender, exchange, cancellation, or termination of previously granted awards. In connection with the establishment of the 2014 Incentive Plan, the Company registered an aggregate of 16,485,333 shares of Common Stock, which corresponds to the number of shares newly available for issuance under the Plan and the aggregate number of shares rolled over into the 2014 Plan from the 2000 Plan as of the shareholder approval date. Employees of the Company, including officers, and nonemployees, including consultants and nonemployee members of the Company's board of directors (collectively, "Participants"), may receive awards as determined by a committee of independent directors ("Committee").
	The awards that may be made under the 2014 Incentive Plan include: (a) Incentive Stock Options ("ISOs") and Nonqualified Stock Options, (b) shares of Restricted Stock, (c) shares of Phantom Stock, (d) Stock Bonuses, and (e) Other Awards.
	Stock Option awards grant Participants the right to purchase shares of Common Stock at prices determined by the Committee; however, in the case of an ISO, the option exercise price will not be less than the fair market value of a share of Common Stock on the date the option is granted. Options vest over a period of time determined by the Committee, generally on a pro rata basis over a three- to four-year period. The Committee also determines the expiration date of each option; however, no ISO is exercisable more than ten years after the date of grant. The maximum term of options that have been awarded under the 2014 Incentive Plan is ten years.
	Restricted Stock awards grant Participants shares of restricted Common Stock or allow Participants to purchase such shares at a price determined by the Committee. Such shares are nontransferable for a period determined by the Committee ("vesting period"). Should employment terminate, as specified in the 2014 Incentive Plan, except as determined by the Committee in its discretion and subject to the applicable 2014 Incentive Plan documents, the ownership of any unvested Restricted Stock will be transferred to the Company. In such an event, the Company will be obligated to repay the Participant the amount, if any, paid by the Participant for such shares. In addition, if the Company requires a return of the Restricted Stock, it also has the right to require a return of all dividends paid on such shares.
	Phantom Stock awards provide the Participant the right to receive, within 30 days of the date on which the share vests, an amount, in cash and/or shares of Common Stock as determined by the Committee, equal to the sum of the fair market value of a share of Common Stock on the date such share of Phantom Stock vests and the aggregate amount of cash dividends paid with respect to a share of Common Stock during the period from the grant date of the share of Phantom Stock to the date on which the share vests. Stock Bonus awards are bonuses payable in shares of Common Stock which are granted at the discretion of the Committee.
	Other Awards are other forms of awards which are valued based on the Common Stock. Subject to the provisions of the 2014 Incentive Plan, the terms and provisions of such Other Awards are determined solely on the authority of the Committee.
	The 2014 Incentive Plan contains provisions that allow for the Committee to provide for the immediate vesting of awards upon a change in control of the Company, as defined in the plan.
	As of December 31, 2014, there were 13,558,022 shares available for future grants under the 2014 Incentive Plan.
	a.	Stock Options
	Transactions involving stock option awards during 2014 under the Company's Incentive Plans are summarized in the table below.
	Stock Options:			Number of Shares			Weighted-Average Exercise Price				Weighted-Average Remaining Contractual Term (in years)	Intrinsic Value (in thousands)
	Outstanding as of December 31, 2013			21,408,268			$	98.1
	2014:00:00	Granted		3,913,368			$	385.33
		Forfeited		(252,126	)		$	155.37
		Expired		(350	)		$	64.35
		Exercised		(3,562,900	)		$	44.72
	Outstanding as of December 31, 2014			21,506,260			$	158.54			6.99	$	5,467,783
	Vested and expected to vest as of December 31, 2014			20,988,044			$	154.81			6.94	$	5,414,258
	Exercisable as of December 31, 2014			12,104,560			$	65.48			5.53	$	4,203,941
	The Company satisfies stock option exercises with newly issued shares of the Company's Common Stock. The total intrinsic value of stock options exercised during 2014, 2013, and 2012 was $1,081.2 million, $727.5 million, and $566.7 million, respectively. The intrinsic value represents the amount by which the market price of the underlying stock exceeds the exercise price of an option.
	The Company grants stock options with exercise prices that are equal to or greater than the average market price of the Company's Common Stock on the date of grant ("Market Price"). The table below summarizes the weighted-average exercise prices and weighted-average grant-date fair values of options issued during the years ended December 31, 2014, 2013, and 2012. The fair value of each option granted under the Company's Incentive Plans during 2014, 2013, and 2012 was estimated on the date of grant using the Black-Scholes option-pricing model.
			Number of Options Granted			Weighted-Average Exercise Price				Weighted-Average Fair Value
	2014:00:00
	Exercise price equal to Market Price		3,913,368			$	385.33			$	140.38
	2013:00:00
	Exercise price equal to Market Price		3,937,989			$	263.77			$	104.9
	2012:00:00
	Exercise price equal to Market Price		4,162,653			$	167.96			$	67.66
	For the years ended December 31, 2014, 2013, and 2012, the Company recognized $291.6 million, $176.4 million, and $67.7 million, respectively, of non-cash stock-based compensation expense related to non-performance based stock option awards. As of December 31, 2014, there was $706.0 million of stock-based compensation cost related to outstanding non-performance based stock options, net of estimated forfeitures, which had not yet been recognized. The Company expects to recognize this compensation cost over a weighted-average period of 1.9 years.
	For the years ended December 31, 2014, 2013, and 2012, the Company recognized $4.1 million, $8.0 million, and $15.3 million, respectively, of non-cash stock-based compensation expense related to performance-based options. The 770,250 performance-based options issued in 2011, which were outstanding and unvested as of December 31, 2013, vested during 2014. There were no additional performance-based options that were unvested as of December 31, 2014.
	Fair Value Assumptions:
	The following table summarizes the weighted average values of the assumptions used in computing the fair value of option grants during 2014, 2013 and 2012.
			2014			2013			2012
	Expected volatility		39	%		42	%		45	%
	Expected lives from grant date		5.2 years			5.3 years			5.4 years
	Expected dividend yield		0	%		0	%		0	%
	Risk-free interest rate		1.62	%		1.73	%		0.86	%
	Expected volatility has been estimated based on actual movements in the Company's stock price over the most recent historical periods equivalent to the options' expected lives. Expected lives are principally based on the Company's historical exercise experience with previously issued employee and board of directors' option grants. The expected dividend yield is zero as the Company has never paid dividends and does not currently anticipate paying any in the foreseeable future. The risk-free interest rates are based on quoted U.S. Treasury rates for securities with maturities approximating the options' expected lives.
	b.	Restricted Stock
	A summary of the Company's activity related to Restricted Stock awards for the year ended December 31, 2014 is summarized below:
	Restricted Stock:			Number of Shares			Weighted-Average Grant Date Fair Value
	Outstanding as of December 31, 2013			538,580			$	112.16
	2014:00:00	Granted		7,500			$	338.32
		Vested		(20	)		$	237.68
	Outstanding as of December 31, 2014			546,060			$	115.26
	The Company recognized non-cash stock-based compensation expense from Restricted Stock awards of $11.5 million, $14.0 million, and $11.1 million in 2014, 2013, and 2012, respectively. As of December 31, 2014, there was $34.5 million of stock-based compensation cost related to unvested shares of Restricted Stock which had not yet been recognized. The Company expects to recognize this compensation cost over a weighted-average period of 2.8 years.

Executive_Stock_Purchase_Plan

Executive Stock Purchase Plan	12 Months Ended
	Dec. 31, 2014
Executive Stock Purchase Plan [Abstract]
Executive Stock Purchase Plan	Executive Stock Purchase Plan
	In 1989, the Company adopted an Executive Stock Purchase Plan (the "Plan") under which 1,027,500 shares of Class A Stock were reserved for restricted stock awards. The Plan provides for the compensation committee of the board of directors to award employees, directors, consultants, and other individuals ("Plan participants") who render service to the Company the right to purchase Class A Stock at a price set by the compensation committee. The Plan provides for the vesting of shares as determined by the compensation committee and, should the Company's relationship with a Plan participant terminate before all shares are vested, unvested shares will be repurchased by the Company at a price per share equal to the original amount paid by the Plan participant. During 1989 and 1990, a total of 983,254 shares were issued, all of which vested as of December 31, 1999. As of December 31, 2014, there were 44,246 shares available for future grants under the Plan.

Employee_Savings_Plan

Employee Savings Plan	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Employee Savings Plan	Employee Savings Plan
	In 1993, the Company adopted the provisions of the Regeneron Pharmaceuticals, Inc. 401(k) Savings Plan (the "Savings Plan"). The terms of the Savings Plan provide for U.S. employees who have met defined service requirements to participate in the Savings Plan by electing to contribute to the Savings Plan a percentage of their compensation to be set aside to pay their future retirement benefits, as defined. The Savings Plan, as amended and restated, provides for the Company to make discretionary contributions ("Contribution"), as defined. The Company recognized $13.1 million, $5.7 million, and $6.3 million of Contribution expense in 2014, 2013, and 2012, respectively.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The Company is subject to U.S. federal, state, and foreign income taxes. Components of income before income taxes consist of the following (foreign income before income taxes in 2012 was not material):
			Year Ended December 31,
			2014				2013
	United States		$	1,115,958			$	812,278
	Foreign		(340,211		)		(98,918		)
			$	775,747			$	713,360
	Components of income tax expense (benefit) consist of the following:
			Year Ended December 31,
			2014				2013			2012
	Current:
		Federal	$	447,370			$	201,475		—
		State	28,718				23,489			$	4,308
		Foreign	2,879				433			—
		Total current tax expense (benefit)	478,967				225,397			4,308
	Deferred:
		Federal	(68,700		)		54,910			(300,319		)
		State	18,891				8,700			(39,837		)
		Foreign	(1,485		)		(9		)	—
		Total deferred tax expense (benefit)	(51,294		)		63,601			(340,156		)
			$	427,673			$	288,998		$	(335,848	)
	In 2014, the Company utilized $448.6 million of net operating loss carry-forwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of ISOs, which were credited to additional paid-in capital as realized.
	In 2013, the Company utilized substantially all of the net operating loss carry-forwards for which deferred tax assets were recorded as of December 31, 2012. The Company also utilized $216.9 million of net operating loss carry-forwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of ISOs, which were credited to additional paid-in capital as realized.
	During the year ended December 31, 2012, substantially all income tax expense relating to the Company's pre-tax income was offset by releasing a portion of the Company's valuation allowance. In addition, in the fourth quarter of 2012, the Company recorded a $340.2 million income tax benefit attributable to the release of substantially all of the remaining valuation allowance against the Company's deferred tax assets. The decision to release this valuation allowance was made after the Company determined that it was more likely than not that these deferred tax assets would be realized, and was based on the evaluation and weighting of positive and negative evidence. For example, in the fourth quarter of 2012, the Company achieved a cumulative three-year income position; a significant positive factor that overcame substantive prior negative evidence. In addition, the Company considered forecasts of future operating results and utilization of net operating losses and tax credits prior to their expiration.
	The Company also recorded an income tax provision in its Statement of Comprehensive Income of $27.1 million during the year ended December 31, 2014 in connection with unrealized gains (losses) on "available-for-sale" marketable securities. For both the years ended December 31, 2013 and 2012, no such income tax provision or benefit was required.
	A reconciliation of the U.S. statutory income tax rate to the Company's effective income tax rate is as follows:
		Year Ended December 31,
		2014			2013			2012
	U.S. federal statutory tax rate	35	%		35	%		35	%
	State and local income taxes	2			3.4			5.4
	Change in state effective rate	2.8			—			5.4
	Foreign income tax rate differential	15.3			4.9			—
	Income tax credits	(7.4	)		(4.9	)		—
	Reclassification of net operating losses related to exercises of stock options	—			—			9.3
	Provision (benefit) attributable to valuation allowances	—			—			(139.0	)
	Provision (benefit) related to uncertain tax positions	2.5			—			—
	Non-deductible Branded Prescription Drug Fee	2.7			1.1			—
	Other permanent differences	2.2			1			2.8
	Effective income tax rate	55.1	%		40.5	%		(81.1	)%
	In 2014, the difference between the U.S. federal statutory rate of 35% and the Company's effective tax rate of 55.1% is primarily attributable to increases related to state and local taxes, the non-deductible Branded Prescription Drug Fee, increases to provisions for uncertain tax positions, and losses incurred in foreign jurisdictions with rates lower than the federal statutory rate. These increases were partially offset by federal and state income tax credits. In December 2014, The Tax Increase Prevention Act of 2014 was enacted, which included a provision to extend the income tax credit for increased research activities retroactively to the tax year ended December 31, 2014. As a result of the extension, the Company recognized the benefit of 2014 federal research tax credit.
	In 2013, the difference between the U.S. federal statutory rate of 35% and the Company's effective tax rate of 40.5% is primarily attributable to increases related to state and local taxes, the non-deductible Branded Prescription Drug Fee, and losses incurred in foreign jurisdictions with rates lower than the federal statutory rate. These increases were partially offset by federal and state income tax credits. In January, 2013, The American Taxpayer Relief Act was enacted, which included a provision to extend the income tax credit for increased research activities retroactively to the tax year ended December 31, 2012, as well as for 2013. As a result of the extension, during 2013, the Company recognized the benefit of both the 2012 and 2013 federal research tax credit, which totaled $34.0 million.
	In 2012, the difference between the U.S. federal statutory rate of 35% and the Company's effective tax rate of (81.1)% was primarily attributable to the benefit of the impact of releasing substantially all of the valuation allowance against deferred tax assets as discussed above, partly offset by increases related to state and local income taxes and non-deductible expenses.
	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company's deferred tax assets and liabilities are as follows:
			As of December 31,
			2014				2013
	Deferred tax assets:
	Net operating loss carry-forward		$	150			$	135
	Fixed assets		8,078				18,902
	Deferred revenue		75,503				88,033
	Deferred compensation		194,489				109,715
	Income tax credit carry-forwards		16,099				9,372
	Capitalized research and development costs		12,908				18,942
	Other		41,252				34,215
			348,479				279,314
	Valuation allowance		(359		)		(1,830		)
	Total deferred tax assets		348,120				277,484
	Deferred tax liabilities:
	Unrealized gains/losses on marketable securities		(28,186		)		—
	Convertible senior notes		(252		)		(929		)
	Other		(3,578		)		—
			(32,016		)		(929		)
	Net deferred tax assets		$	316,104			$	276,555
	In 2014, the Company's deferred tax assets increased primarily due to increases in assets related to deferred compensation and tax credit carryforwards. These increases in deferred tax assets were partly offset by decreases in assets related to fixed assets, capitalized research and development costs, and deferred revenue. At December 31, 2014, the Company retained a valuation allowance against certain state tax credits and other tax-related carry-forwards, as the realizability of these deferred tax assets within the carry-forward period is uncertain. The Company's deferred tax liabilities increased due to the tax impact of changes in unrealized gains (loss) on available-for-sale marketable securities.
	In 2013, the Company's net deferred tax assets (before valuation allowance) decreased compared to the prior year primarily due to utilization of the deferred tax assets relating to net operating loss carry-forward and tax credits to offset tax liabilities associated with the Company's 2013 pre-tax income. These decreases in deferred tax assets were partially offset by increases in the deferred tax assets related to deferred compensation.
The Company expects to use its remaining federal net operating loss carry-forwards, which will expire in various years from 2018 to 2032, in connection with its 2014 income tax return. The tax benefit of these net operating loss carry-forwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of Incentive Stock Options, which are credited to additional paid-in capital when realized. The Internal Revenue Code contains certain provisions that can limit a taxpayer's ability to utilize net operating losses and tax credit carry-forwards in any given year resulting from cumulative changes in ownership interests in excess of 50% over a three-year period. The Company does not believe, however, that any such limitation would have a significant impact on the Company's ability to utilize its net operating losses or income tax credit carry-forwards prior to expiration.
The Company's 2012 and 2013 federal income tax returns remain open to examination by the IRS. In 2014, U.S. federal tax authorities concluded an examination of the Company's 2011 federal income tax return with no material adjustments. The Company's 2012 federal income tax return is currently under audit by the IRS. During 2014, New York State tax authorities finalized their audit of the Company's 2009, 2010, and 2011 business corporation franchise tax returns with no adjustments. The United States and many states generally have statutes of limitation ranging from 3 to 5 years; however, those statutes could be extended due to the Company's net operating loss and tax credit carry-forward positions in a number of the Company's tax jurisdictions. In general, tax authorities have the ability to review income tax returns for loss periods in which the statute of limitation has previously expired to adjust the net operating loss carry-forward or tax credits generated in those years.
The following table summarizes the gross amounts of unrecognized tax benefits, without regard to reduction in tax liabilities or additions to deferred tax assets and liabilities if such unrecognized tax benefits were settled. The amount, if recognized, that would impact the effective tax rate is $51.2 million, $23.5 million, and $8.4 million as of December 31, 2014, 2013, and 2012, respectively.
		2014				2013			2012
Balance as of January 1		$	26,627			$	11,274		$	5,596
Gross increases related to current year tax positions		27,538				7,620			1,873
Gross increases related to prior year tax positions		6,464				8,305			3,805
Gross decrease due to settlements, recapture, filed returns, and lapse of statutes of limitation		(3,014		)		(572		)	—
Balance as of December 31		$	57,615			$	26,627		$	11,274
In 2014, the increase in unrecognized tax benefits related primarily to the Company’s calculation of certain tax credits and other items related to the Company's international operations, while the decreases resulted from the settlement of the IRS audit of the 2011 tax year and the New York State audit of the 2009 to 2011 tax years, as well as the reduction in the New York state income tax rate. In 2013 and 2012, the increase in unrecognized tax benefits related primarily to the Company's calculation of certain tax credits. Due to the amounts of the Company's net operating loss and tax credit carry-forwards, the Company has not accrued material interest or penalties related to these unrecognized tax benefits. The Company believes that it is reasonably possible that its unrecognized tax benefits at December 31, 2014 may increase within the next twelve months relating to operations during that period, in excess of potential decreases due to the resolution of the federal audit.

Legal_Matters

Legal Matters	12 Months Ended
	Dec. 31, 2014
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.
	Proceedings Relating to '287 Patent and '018 Patent
	The Company is a party to patent infringement litigation involving its European Patent No. 1,360,287 (the "'287 Patent") and its U.S. Patent No. 8,502,018 (the "'018 Patent"), both of which concern genetically altered 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 "'287 Patent Infringement Litigation" and "'018 Patent Infringement Litigation," respectively), the Company claims infringement of several claims of the '287 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 and the '018 Patent (as applicable). At this time the Company is not able to predict the outcome of, or an estimate of gain, if any, related to, these proceedings. With respect to the '018 Patent Infringement Litigation against Ablexis, LLC, on October 31, 2014, the Company and Ablexis reached a confidential settlement and filed a joint stipulation dismissing the action with prejudice.
	Proceedings Relating to PCSK9 Antibody (PRALUENT)
	On October 17, 2014 and October 28, 2014, Amgen Inc. filed complaints against Regeneron, Sanofi, Aventisub LLC (subsequently removed and replaced with Sanofi-Aventis U.S. LLC), and Aventis Pharmaceuticals, Inc. in the United States District Court for the District of Delaware seeking an injunction to prevent Regeneron and the other defendants from manufacturing, using, offering to sell, or selling within the United States (as well as importing into the United States) PRALUENT, the antibody to PCSK9 for LDL cholesterol reduction Regeneron is jointly developing with Sanofi. On November 11, 2014 and November 17, 2014 Amgen filed complaints against Regeneron, Sanofi, Sanofi-Aventis U.S. LLC, and Aventis Pharmaceuticals, Inc. in the same court seeking the same relief. Amgen asserts U.S. Patent Nos. 8,563,698, 8,829,165, and 8,859,741 in the first complaint, U.S. Patent Nos. 8,871,913 and 8,871,914 in the second complaint, U.S. Patent No. 8,883,983 in the third complaint, and U.S. Patent No. 8,889,834 in the fourth complaint. 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. On December 15, 2014, all of the four proceedings were consolidated into a single case. This matter has not yet progressed sufficiently through discovery and/or development of important factual information and legal issues to enable the Company to estimate a range of possible loss, if any.

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	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:
		December 31,
		2014			2013			2012
	Net income - basic	$	348,074		$	424,362		$	750,269
	Effect of dilutive securities:
	Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs	—			—			29,126
	Net income - diluted	$	348,074		$	424,362		$	779,395
	(Shares in thousands)
	Weighted average shares - basic	100,612			97,917			94,685
	Effect of dilutive securities:
	Stock options	9,440			10,233			14,231
	Restricted stock	425			433			715
	Convertible senior notes	—			—			4,761
	Warrants	2,936			2,707			990
	Dilutive potential shares	12,801			13,373			20,697
	Weighted average shares - diluted	113,413			111,290			115,382
	Net income per share - basic	$	3.46		$	4.33		$	7.92
	Net income per share - diluted	$	3.07		$	3.81		$	6.75
	Shares which have been excluded from the December 31, 2014, 2013, and 2012 diluted per share amounts because their effect would have been antidilutive, include the following:
		December 31,
	(Shares in thousands)	2014		2013			2012
	Stock options	1,470		304			325
	Convertible senior notes	4,247		4,761			—

Statement_of_Cash_Flows

Statement of Cash Flows	12 Months Ended
	Dec. 31, 2014
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 December 31, 2014, 2013, and 2012 were $56.2 million, $16.1 million, and $8.6 million, respectively, of accrued capital expenditures. Accrued capital expenditures as of December 31, 2014 were primarily related to renovation of the Company's new Limerick, Ireland facility and expansion and renovations in its Rensselaer, New York manufacturing facilities.
	Included in accounts payable and accrued expenses as of December 31, 2014 was $7.5 million in connection with the Company's conversion settlement obligation related to the Company's convertible senior notes (see Note 12). No such amounts were payable as of December 31, 2013 and 2012.
	Included in accounts payable and accrued expenses as of December 31, 2014 was $59.8 million related to the Company's payment obligation for a reduction in the number of warrants based on a warrant holder closing out a portion of its hedge position (see Note 12). Additionally, included within other current liabilities was $87.5 million in connection with the estimated fair value of the remaining warrant liability as of December 31, 2014 (see Note 12). There were no such liabilities recorded in connection with warrants as of December 31, 2013 and 2012.
	The Company recognized a facility lease obligation of $127.8 million and $25.0 million during 2014 and 2013, respectively, in connection with capitalizing, on the Company's books, the landlord's costs of constructing new facilities that the Company has leased (see Note 13a). The Company did not recognize any such facility lease obligations during 2012.
	Included in property, plant, and equipment as of December 31, 2014 and 2013 were $6.2 million and $1.9 million of capitalized interest for the years ended December 31, 2014 and 2013, respectively, as the related facilities are currently under construction. For the year ended December 31, 2012, the Company did not capitalize any interest.

Unaudited_Quarterly_Results

Unaudited Quarterly Results	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Results	Unaudited Quarterly Results
	Summarized quarterly financial data for the years ended December 31, 2014 and 2013 are set forth in the following tables.
		First Quarter Ended		Second Quarter Ended		Third Quarter Ended		Fourth Quarter Ended
		31-Mar-14		30-Jun-14		30-Sep-14		31-Dec-14
		(Unaudited)
	Revenues (1)	$	625,740	$	665,700	$	725,788	$	802,329
	Net income (2)	$	65,443	$	92,735	$	79,720	$	110,176
	Net income per share - basic	$	0.66	$	0.92	$	0.79	$	1.09
	Net income per share - diluted	$	0.58	$	0.82	$	0.7	$	0.96
		First Quarter Ended		Second Quarter Ended		Third Quarter Ended		Fourth Quarter Ended
		31-Mar-13		30-Jun-13		30-Sep-13		31-Dec-13
		(Unaudited)
	Revenues (3)	$	439,664	$	457,642	$	597,027	$	610,412
	Net income	$	98,874	$	87,376	$	141,306	$	96,806
	Net income per share - basic	$	1.02	$	0.89	$	1.44	$	0.98
	Net income per share - diluted	$	0.9	$	0.79	$	1.25	$	0.86
	(1) Revenues in the first, second, third, and fourth quarters of 2014 included recognition of sales milestones of $30.0 million, $15.0 million, $30.0 million, and $30.0 million, respectively.
	(2) Net income in the third quarter of 2014 included a $40.6 million incremental charge related to the Branded Prescription Drug Fee based on final regulations issued by the IRS in July 2014 as described in Note 3 above.
	(3) Revenues in the second quarter of 2013 were reduced by two $10 million up-front payments made to Sanofi to acquire full rights to antibodies to PDGF and antibodies to Ang2 in ophthalmology, as described in Note 4 above. Revenues in the third and fourth quarter of 2013 included recognition of sales and substantive development milestones of $45.0 million and $25.0 million, respectively.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Consolidation	Basis of Presentation
	The consolidated financial statements include the accounts of Regeneron and its wholly-owned subsidiaries. Intercompany balances and transactions are eliminated in consolidation.
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Estimates which could have a significant impact on the Company's financial statements include provisions related to product sales, such as rebates, chargebacks, and distribution-related fees; periods over which payments, including non-refundable up-front, license, and milestone payments, are recognized as revenue in connection with collaboration and other agreements; periods over which certain clinical trial costs are recognized; fair value of stock options; inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value; capitalization of inventory costs associated with the Company's products prior to regulatory approval; deferred tax asset valuation allowance; and the assessment of uncertain tax positions.
	With respect to the Company's collaborations with Sanofi and Bayer HealthCare:
	•	Included in Sanofi collaboration revenue is the Company's share of profits or losses from commercialization of ZALTRAP and commercialization of antibodies, which are provided by Sanofi, and include an estimate of the Company's share of profits or losses for the most recent fiscal quarter.
	•	Included in Bayer HealthCare collaboration revenue is the Company's share of profits or losses from commercialization of EYLEA outside the United States, which is provided by Bayer HealthCare, and includes an estimate of the Company's share of profits or losses for the most recent fiscal quarter.
	•	Included in research and development expenses is the Company's share of development expenses incurred by its collaborators, Bayer HealthCare and Sanofi, including the Company's share of Bayer HealthCare and Sanofi estimated development expenses for the most recent fiscal quarter.
	These estimates for the most recent period are adjusted, if necessary, in the subsequent period to reflect actual amounts.
Cash and Cash Equivalents	Cash and Cash Equivalents
	The Company considers all highly liquid debt instruments with a maturity of three months or less when purchased to be cash equivalents. The carrying amount reported in the Balance Sheet for cash and cash equivalents approximates its fair value.
Marketable Securities	Marketable Securities
	The Company has an investment policy that includes guidelines on acceptable investment securities, minimum credit quality, maturity parameters, and concentration and diversification. The Company invests its excess cash primarily in marketable securities issued by investment grade institutions. The Company considers its marketable securities to be "available-for-sale," as defined by authoritative guidance issued by the Financial Accounting Standards Board ("FASB"). These assets are carried at fair value and the unrealized gains and losses are included in accumulated other comprehensive income (loss). If a decline in the value of a marketable security in the Company's investment portfolio is deemed to be other-than-temporary, the Company writes down the security to its current fair value and recognizes a loss as a charge against income. The Company reviews its portfolio of marketable securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost are other-than-temporary.
Accounts Receivable - Trade	Accounts Receivable - Trade
	The Company's trade accounts receivable arise from product sales and represent amounts due from its distributors and specialty pharmacies (collectively, the Company's "customers"), which are all located in the United States. The Company monitors the financial performance and credit worthiness of its large customers so that it can properly assess and respond to changes in their credit profile. The Company provides reserves against trade receivables for estimated losses, if any, that may result from a customer's inability to pay. Amounts determined to be uncollectible are written-off against the reserve.
Inventories	Inventories
	Inventories are stated at the lower of cost or estimated realizable value. The Company determines the cost of inventory using the first-in, first-out, or FIFO, method.
	The Company capitalizes inventory costs associated with the Company's products prior to regulatory approval when, based on management's judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed as research and development. The determination to capitalize inventory costs is based on various factors, including status and expectations of the regulatory approval process, any known safety or efficacy concerns, potential labeling restrictions, and any other impediments to obtaining regulatory approval.
	The Company periodically analyzes its inventory levels to identify inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value, and writes-down such inventories as appropriate. In addition, the Company's products are subject to strict quality control and monitoring which the Company performs throughout the manufacturing process. If certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, the Company records a charge to cost of goods sold to write down such unmarketable inventory to its estimated realizable value.
Property, Plant and Equipment	Property, Plant, and Equipment
	Property, plant, and equipment are stated at cost, net of accumulated depreciation. Depreciation is provided on a straight-line basis over the estimated useful lives of the assets. Costs of construction of certain long-lived assets include capitalized interest, which is amortized over the estimated useful life of the related asset. Expenditures for maintenance and repairs which do not materially extend the useful lives of the assets are charged to expense as incurred. The cost and accumulated depreciation or amortization of assets retired or sold are removed from the respective accounts, and any gain or loss is recognized in operations. The estimated useful lives of property, plant, and equipment are as follows:
	Building and improvements		10-30 years
	Laboratory and other equipment		3-10 years
	Furniture and fixtures		5 years
	The Company periodically assesses the recoverability of long-lived assets, such as property, plant, and equipment, and evaluates such assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Asset impairment is determined to exist if estimated future undiscounted cash flows are less than the carrying amount.
Revenue Recognition - Product Revenue	Product Revenue
	Product sales consist of U.S. sales of EYLEA and ARCALYST. Revenue from product sales is recognized when persuasive evidence of an arrangement exists, title to product and associated risk of loss have passed to the customer, the price is fixed or determinable, collection from the customer is reasonably assured, the Company has no further performance obligations, and returns can be reasonably estimated. The Company's written contracts with its customers stipulate product is shipped freight on board destination (FOB destination). The Company records revenue from product sales upon delivery to its customers.
	The Company sells EYLEA in the United States to several distributors and specialty pharmacies. The Company sells ARCALYST in the United States to two specialty pharmacies. Under these distribution models, the distributors and specialty pharmacies generally take physical delivery of product. For EYLEA, the distributors and specialty pharmacies generally sell the product directly to healthcare providers, whereas for ARCALYST, the specialty pharmacies sell the product directly to patients.
	Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks under governmental programs, distribution-related fees, prompt pay discounts, product returns, and other sales-related deductions. Calculating these provisions involves estimates and judgments. The Company reviews its estimates of rebates, chargebacks, and other applicable provisions each period and records any necessary adjustments in the current period's net product sales.
	Government Rebates and Chargebacks: The Company estimates reductions to product sales for Medicaid and Veterans' Administration ("VA") programs, and for certain other qualifying federal and state government programs. Based upon the Company's contracts with government agencies, statutorily-defined discounts applicable to government-funded programs, historical experience, and estimated payer mix, the Company estimates and records an allowance for rebates and chargebacks. The Company's liability for Medicaid rebates consists of estimates for claims that a state will make for a current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, and invoices received for claims from prior quarters that have not been paid. The Company's reserves related to discounted pricing to VA, Public Health Services ("PHS"), and other institutions (collectively "qualified healthcare providers") represent the Company's estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices the Company charges to its customers (i.e., distributors and specialty pharmacies). The Company's customers charge the Company for the difference between what they pay for the products and the ultimate selling price to the qualified healthcare providers. The Company's reserve for this discounted pricing is based on expected sales to qualified healthcare providers and the chargebacks that customers have already claimed.
	Distribution-Related Fees: The Company has written contracts with its customers that include terms for distribution-related fees. The Company estimates and records distribution and related fees due to its customers based on gross sales.
	Prompt Pay Discounts: No prompt pay discounts are currently offered to the Company's customers on sales of EYLEA. In connection with sales of ARCALYST, the Company offers discounts to its customers for prompt payments. The Company estimates these discounts based on customer terms and historical experience, and expects that its customers will always take advantage of this discount. Therefore, the Company accrues 100% of the prompt pay discount that is based on the gross amount of each ARCALYST invoice, at the time of sale.
	Product Returns: Consistent with industry practice, the Company offers its customers a limited right to return product purchased directly from the Company, which is principally based upon the product's expiration date. The Company will accept returns for three months prior to and up to six months after the product expiration date. Product returned is generally not resalable given the nature of the Company's products and method of administration. The Company develops estimates for product returns based upon historical experience, inventory levels in the distribution channel, shelf life of the product, and other relevant factors. The Company monitors product supply levels in the distribution channel, as well as sales by its customers of EYLEA to healthcare providers and ARCALYST to patients using product-specific data provided by its customers. If necessary, the Company's estimates of product returns may be adjusted in the future based on actual returns experience, known or expected changes in the marketplace, or other factors.
Revenue Recognition - Collaboration Revenue	Collaboration Revenue
	The Company earns collaboration revenue in connection with collaboration agreements to develop and commercialize product candidates and utilize the Company's technology platforms. These arrangements may require the Company to deliver various rights, services, and/or goods across the entire life cycle of a product or product candidate. The terms of these agreements typically include that consideration be provided to the Company in the form of non-refundable up-front licensing payments, research progress (milestone) payments, payments for development and commercialization activities, and sharing of profits or losses arising from the commercialization of products. In arrangements involving multiple deliverables, each required deliverable is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is generally based on whether the deliverables in the arrangement meet certain criteria, including whether the delivered item or items has value to the collaborator on a standalone basis. The arrangement's consideration that is fixed and determinable is allocated to each separate unit of accounting based on the relative selling price of each deliverable. If multiple collaboration activities or rights do not require separation, they are combined into a single unit of accounting and recognized over the performance period, which is the period over which the Company is obligated to deliver goods or services. Historically, non-refundable up-front license payments, where continuing involvement is required of the Company, have been deferred and recognized over the related performance period. The Company estimates its performance period based on the specific terms of each agreement, and adjusts the performance periods, if appropriate, based on the applicable facts and circumstances. Payments which are based on achieving a specific substantive performance milestone, involving a degree of risk, are recognized as revenue when the milestone is achieved and the related payment is due and non-refundable, provided there is no future service obligation associated with that milestone. Substantive performance milestones typically consist of significant achievements in the development life-cycle of the related product candidate, such as completion of clinical trials, filing for approval with regulatory agencies, and receipt of approvals by regulatory agencies. In determining whether a payment is deemed to be a substantive performance milestone, the Company takes into consideration (i) the enhancement in value to the related development product candidate, (ii) the Company's performance and the relative level of effort required to achieve the milestone, (iii) whether the milestone relates solely to past performance, and (iv) whether the milestone payment is considered reasonable relative to all of the deliverables and payment terms. Payments for achieving milestones which are not considered substantive are deferred and recognized over the related performance period.
	The Company enters into collaboration agreements that include varying arrangements regarding which parties perform and bear the costs of research and development activities. The Company may share the costs of research and development activities with a collaborator, or the Company may be reimbursed for all or a significant portion of the costs of the Company's research and development activities. The Company records its internal and third-party development costs associated with these collaborations as research and development expenses. When the Company is entitled to reimbursement of all or a portion of the research and development expenses that it incurs under a collaboration, the Company records those reimbursable amounts as collaboration revenue proportionately as the Company recognizes its expenses. If the collaboration is a cost-sharing arrangement in which both the Company and its collaborator perform development work and share costs, the Company also recognizes, as additional research and development expense in the period when its collaborator incurs development expenses, the portion of the collaborator's development expenses that the Company is obligated to reimburse. The Company may also be obligated to use commercially reasonable efforts to supply commercial bulk product to its collaborators. In such cases, the Company is reimbursed for its manufacturing costs as commercial product is shipped to its collaborators; however, recognition of such cost reimbursements as collaboration revenue is deferred until the product is sold by the Company's collaborators to third-party customers, at which time the Company's risk of inventory loss no longer exists. In addition, at that time, the related manufacturing costs for the sold product, which had been capitalized into inventory, are recognized by the Company.
	Under the Company's collaboration agreements, product sales and cost of sales for products which are currently approved are recorded by the Company's collaborators. The Company shares in any profits or losses arising from the commercialization of such products. The Company records its share of the profits or losses from commercialization of such products, representing net product sales less cost of goods sold and shared commercialization and other expenses, as collaboration revenue.
	In connection with non-refundable licensing payments, the Company's performance period estimates are principally based on projections of the scope, progress, and results of its research and development activities. Due to the variability in the scope of activities and length of time necessary to develop a drug product, changes to development plans as programs progress, and uncertainty in the ultimate requirements to obtain governmental approval for commercialization, revisions to performance period estimates are likely to occur periodically, and could result in material changes to the amount of revenue recognized each year in the future. In addition, estimated performance periods may change if development programs encounter delays, or the Company and its collaborators decide to expand or contract the clinical plans for a drug candidate in various disease indications.
Revenue Recognition - Technology Licensing	VelocImmune® Technology Licensing
	The Company enters into non-exclusive license agreements with third parties that allow the third party to utilize the Company's VelocImmune technology in its internal research programs. The terms of these agreements may include up-front payments and entitle the Company to receive royalties on any future sales of products discovered by the third party using the Company's VelocImmune technology. Up-front payments under these agreements, where continuing involvement is required of the Company, are deferred and recognized ratably over their respective license periods.
Research and Development Expenses	Research and Development Expenses
	Research and development expenses include costs directly attributable to the conduct of research and development programs, including the cost of salaries, payroll taxes, employee benefits, materials, supplies, depreciation on and maintenance of research equipment, costs related to research collaboration and licensing agreements, the cost of services provided by outside contractors, including services related to the Company's clinical trials, clinical trial expenses, the full cost of manufacturing drug for use in research, preclinical development, and clinical trials, amounts that the Company is obligated to reimburse to collaborators for research and development expenses that they incur, and the allocable portions of facility costs, such as rent, utilities, insurance, repairs and maintenance, depreciation, and general support services. All costs associated with research and development are expensed.
	Clinical trial costs are a significant component of research and development expenses and include costs associated with third-party contractors. The Company outsources a substantial portion of its clinical trial activities, utilizing external entities such as contract research organizations ("CROs"), independent clinical investigators, and other third-party service providers to assist the Company with the execution of its clinical studies. For each clinical trial that the Company conducts, certain clinical trial costs are expensed immediately, while others are expensed over time based on the expected total number of patients in the trial, the rate at which patients enter the trial, and/or the period over which clinical investigators or CROs are expected to provide services.
	Clinical activities which relate principally to clinical sites and other administrative functions to manage the Company's clinical trials are performed primarily by CROs. CROs typically perform most of the start-up activities for the Company's trials, including document preparation, site identification, screening and preparation, pre-study visits, training, and program management. These start-up costs usually occur within a few months after the contract has been executed and are event driven in nature. The remaining activities and related costs, such as patient monitoring and administration, generally occur ratably throughout the life of the individual contract or study. In the event of early termination of a clinical trial, the Company accrues and recognizes expenses in an amount based on its estimate of the remaining non-cancelable obligations associated with the winding down of the clinical trial and/or penalties.
	For clinical study sites, where payments are made periodically on a per-patient basis to the institutions performing the clinical study, the Company accrues expenses on an estimated cost-per-patient basis, based on subject enrollment and activity in each quarter. The amount of clinical study expense recognized in a quarter may vary from period to period based on the duration and progress of the study, the activities to be performed by the sites each quarter, the required level of patient enrollment, the rate at which patients actually enroll in and drop-out of the clinical study, and the number of sites involved in the study. Clinical trials that bear the greatest risk of change in estimates are typically those that have a significant number of sites, require a large number of patients, have complex patient screening requirements, and span multiple years. During the course of a trial, the Company adjusts its rate of clinical expense recognition if actual results differ from the Company's estimates. The Company's estimates and assumptions for clinical expense recognition could differ significantly from its actual results, which could cause material increases or decreases in research and development expenses in future periods when the actual results become known.
Stock-based Compensation	Stock-based Compensation
	The Company recognizes stock-based compensation expense for grants of stock option awards and restricted stock under the Company's Long-Term Incentive Plan to employees and non-employee members of the Company's board of directors based on the grant-date fair value of those awards. The grant-date fair value of an award is generally recognized as compensation expense over the award's requisite service period. In addition, the Company has granted performance-based stock option awards which vest based upon the optionee satisfying certain performance and service conditions as defined in the agreements. Potential compensation cost, measured on the grant date, related to these performance options will be recognized only if, and when, the Company estimates that these options will vest, which is based on whether the Company considers the options' performance conditions to be probable of attainment. The Company's estimates of the number of performance-based options that will vest will be revised, if necessary, in subsequent periods.
	The Company uses the Black-Scholes model to compute the estimated fair value of stock option awards. Using this model, fair value is calculated based on assumptions with respect to (i) expected volatility of the Company's Common Stock price, (ii) the periods of time over which employees and members of the board of directors are expected to hold their options prior to exercise (expected lives), (iii) expected dividend yield on the Common Stock, and (iv) risk-free interest rates. Stock-based compensation expense also includes an estimate, which is made at the time of grant, of the number of awards that are expected to be forfeited. This estimate is revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
Income Taxes	Income Taxes
	The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined on the basis of the difference between the tax basis of assets and liabilities and their respective financial reporting amounts ("temporary differences") at enacted tax rates in effect for the years in which the differences are expected to reverse. A valuation allowance is established for deferred tax assets for which it is more likely than not that some portion or all of the deferred tax assets will not be realized.
	Uncertain tax positions are accounted for in accordance with FASB authoritative guidance, which prescribes a comprehensive model for the manner in which a company should recognize, measure, present, and disclose in its financial statements all material uncertain tax positions that the company has taken or expects to take on a tax return. Those positions, for which management's assessment is that there is more than a 50% probability of sustaining the position upon challenge by a taxing authority based upon its technical merits, are subjected to certain measurement criteria.
	The Company's policy is to recognize interest and penalties related to income tax matters in income tax expense.
Per Share Data	Per Share Data
	Basic net income per share is 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. Basic net income per share excludes restricted stock awards until vested. Diluted net income per share includes the potential dilutive effect of common stock equivalents as if such securities were converted or exercised during the period, when the effect is dilutive. Common stock equivalents include: (i) outstanding stock options and restricted stock awards under the Company's Long-Term Incentive Plans, which are included under the "treasury stock method" when dilutive, (ii) Common Stock to be issued upon the assumed conversion of the Company's convertible senior notes, which are included under the "if-converted method" when dilutive, and (iii) Common Stock to be issued upon the exercise of outstanding warrants, which are included under the "treasury stock method" when dilutive.
Concentration of Credit Risk	Concentration of Credit Risk
	Financial instruments which potentially expose the Company to concentrations of credit risk consist of cash, cash equivalents, certain financial instruments, and accounts receivable. A large portion of the Company's cash is held by a few major financial institutions. In accordance with the Company's policies, the Company mandates asset diversification and monitors exposure with its counterparties.
	Concentrations of credit risk with respect to accounts receivable are significant. Accounts receivable from product sales of EYLEA and ARCALYST are due from several distributors and specialty pharmacies, who are the Company's customers. As of December 31, 2014 and 2013, one individual customer accounted for 70% and 75%, respectively, of the Company's net trade accounts receivable balances. The Company has contractual payment terms with each of its customers, and the Company monitors its customers' financial performance and credit worthiness so that it can properly assess and respond to any changes in their credit profile. In addition, the Company may insure a portion of its accounts receivables within its overall risk management practices. As of December 31, 2014 and 2013, there were no reserves against trade accounts receivable. In addition, during the years ended December 31, 2014, 2013, and 2012, the Company did not recognize any charges for write-offs of trade accounts receivable.
Reclassifications	Reclassifications
	Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.
Recently Issued Accounting Standards	Recently Issued Accounting Standards
	In May 2014, the FASB issued a new standard related to revenue recognition, Revenue from Contracts with Customers, which 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, 2016, and early adoption is not permitted. The standard allows for two transition methods - retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial adoption. The Company has not yet determined its method of transition and is evaluating the impact that this guidance will have on the Company's financial statements.
Legal Costs	Costs associated with the Company's involvement in legal proceedings are expensed as incurred.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Estimated Useful Lives of Property, Plant, and Equipment	The estimated useful lives of property, plant, and equipment are as follows:
	Building and improvements	10-30 years
	Laboratory and other equipment	3-10 years
	Furniture and fixtures	5 years

Net_Product_Sales_Tables

Net Product Sales (Tables)	12 Months Ended
	Dec. 31, 2014
Revenues [Abstract]
Sales Related Deductions Activity	The following table summarizes the provisions, and credits/payments, for these sales-related deductions for the years ended December 31, 2014, 2013, and 2012.
		Rebates &			Distribution-			Other Sales-			Total
		Chargebacks			Related			Related
					Fees			Deductions
	Balance as of December 31, 2011	$	585		$	1,451		$	182		$	2,218
	Provision related to current period sales	14,153			45,028			3,070			62,251
	Credits/payments	(11,755		)	(31,181		)	(2,707		)	(45,643		)
	Balance as of December 31, 2012	2,983			15,298			545			18,826
	Provision related to current period sales	25,936			62,984			955			89,875
	Credits/payments	(24,519		)	(58,619		)	(962		)	(84,100		)
	Balance as of December 31, 2013	4,400			19,663			538			24,601
	Provision related to current period sales	33,117			77,160			1,578			111,855
	Credits/payments	(34,434		)	(75,657		)	(1,584		)	(111,675		)
	Balance as of December 31, 2014	$	3,083		$	21,166		$	532		$	24,781

Collaboration_Agreements_Table

Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2014
Collaboration Agreement [Abstract]
Schedule of Related Party Transactions [Table Text Block]	The collaboration revenue the Company earned from Sanofi is detailed below:
		Year Ended December 31,
	Sanofi Collaboration Revenue	2014			2013			2012
	ZALTRAP:
	Regeneron's share of losses in connection with commercialization of ZALTRAP	$	(4,715	)	$	(30,810	)	$	(25,634	)
	Substantive milestone	—			—			50,000
	Reimbursement of Regeneron research and development expenses	4,806			5,639			10,702
	Other	5,102			9,682			13,268
	Total ZALTRAP	5,193			(15,489		)	48,336
	Antibody:
	Reimbursement of Regeneron research and development expenses	547,761			453,489			365,245
	Reimbursement of Regeneron commercialization-related expenses	19,480			1,868			—
	Regeneron's share of losses in connection with commercialization of antibodies	(41,378		)	—			—
	Up-front payments to Sanofi for acquisition of rights related to two antibodies	—			(20,000		)	—
	Other	10,243			10,243			10,233
	Total Antibody	536,106			445,600			375,478
		$	541,299		$	430,111		$	423,814
Collaboration revenue	The collaboration revenue the Company earned from Bayer HealthCare is detailed below:
		Year Ended December 31,
	Bayer HealthCare Collaboration Revenue	2014			2013			2012
	EYLEA:
	Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	301,302		$	101,494		—
	Sales and substantive development milestones	105,000			70,000			$	25,000
	Cost-sharing of Regeneron EYLEA development expenses	23,383			20,905			34,892
	Other	52,390			27,890			10,207
	Total EYLEA	482,075			220,289			70,099
	PDGFR-beta antibody:
	Cost-sharing of REGN2176-3 development expenses	2,848			—			—
	Other	10,632			—			—
	Total PDGFR-beta	13,480			—			—
		$	495,555		$	220,289		$	70,099

Marketable_Securities_Tables

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2014
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 December 31, 2014		Cost Basis			Gains			Losses			Value
	Unrestricted
	Corporate bonds		$	548,832		$	136		$	(1,462	)	$	547,506
	U.S. government and government agency obligations		28,596			3			(46		)	28,553
	Municipal bonds		37,044			37			(43		)	37,038
	Equity securities		2,005			5,374			—			7,379
			616,477			5,550			(1,551		)	620,476
	Restricted
	Equity securities		15,000			76,439			—			91,439
			$	631,477		$	81,989		$	(1,551	)	$	711,915
	As of December 31, 2013
	Unrestricted
	Corporate bonds		$	369,321		$	233		$	(361	)	$	369,193
	U.S. government and government agency obligations		107,493			55			(27		)	107,521
	Commercial paper		23,891			53			—			23,944
	Municipal bonds		36,935			45			(59		)	36,921
	International government agency obligations		2,007			1			—			2,008
	Certificates of deposit		7,509			5			—			7,514
	Equity securities		1,166			—			—			1,166
			$	548,322		$	392		$	(447	)	$	548,267
Marketable Securities, Based on Contractual Maturity Dates	The fair values of debt security investments by contractual maturity consist of the following:
			As of December 31,
			2014			2013
	Maturities within one year		$	251,761		$	158,376
	Maturities after one year through five years		360,208			383,410
	Maturities after five years through ten years		1,128			4,138
	Maturities after ten years		—			1,177
			$	613,097		$	547,101
Fair Value and Unrealized Losses of Marketable Securities	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 December 31, 2014	Fair Value			Unrealized Loss			Fair Value			Unrealized Loss		Fair Value		Unrealized Loss
	Corporate bonds	$	390,613		$	(1,462	)	—			—		$	390,613	$	(1,462	)
	U.S. government and government agency obligations	25,549			(46		)	—			—		25,549		(46		)
	Municipal bonds	10,779			(43		)	—			—		10,779		(43		)
		$	426,941		$	(1,551	)	—			—		$	426,941	$	(1,551	)
	As of December 31, 2013
	Corporate bonds	$	176,140		$	(361	)	—			—		$	176,140	$	(361	)
	U.S. government and government agency obligations	49,241			(27		)	—			—		49,241		(27		)
	Municipal bonds	14,431			(59		)	—			—		14,431		(59		)
		$	239,812		$	(447	)	—			—		$	239,812	$	(447	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
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 December 31, 2014	Fair Value		Quoted Prices in		Significant Other
				Active Markets		Observable Inputs
				for Identical		(Level 2)
				Assets
				(Level 1)
	Available-for-sale marketable securities:
	Unrestricted
	Corporate bonds	$	547,506	—		$	547,506
	U.S. government and government agency obligations	28,553		—		28,553
	Municipal bonds	37,038		—		37,038
	Equity securities	7,379		$	7,379	—
		620,476		7,379		613,097
	Restricted
	Equity securities	91,439		—		91,439
		$	711,915	$	7,379	$	704,536
	As of December 31, 2013
	Available-for-sale marketable securities:
	Unrestricted
	Corporate bonds	$	369,193	—		$	369,193
	U.S. government and government agency obligations	107,521		—		107,521
	Commercial paper	23,944		—		23,944
	Municipal bonds	36,921		—		36,921
	International government agency obligations	2,008		—		2,008
	Certificates of deposit	7,514		—		7,514
	Equity securities	1,166		$	1,166	—
		$	548,267	$	1,166	$	547,101

Inventory_Tables

Inventory (Tables)	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	Inventories consist of the following:
		As of December 31,
		2014		2013
	Raw materials	$	10,923	$	9,120
	Work-in-process	73,519		35,868
	Finished goods	10,768		14,352
	Deferred costs	33,651		11,014
		$	128,861	$	70,354

Property_Plant_and_Equipment_T

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant, and equipment consist of the following:
		As of December 31,
		2014			2013
	Land	$	2,768		$	2,768
	Building and improvements	398,981			343,363
	Leasehold improvements	42,600			26,370
	Construction-in-progress	472,231			142,370
	Laboratory and other equipment	253,058			189,543
	Furniture, computer and office equipment, and other	58,655			44,186
		1,228,293			748,600
	Less, accumulated depreciation and amortization	(253,984		)	(221,617		)
		$	974,309		$	526,983

Accounts_Payable_and_Accrued_E1

Accounts Payable and Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Schedule of Accounts Payable and Accrued Liabilities	Accounts payable and accrued expenses consist of the following:
		As of December 31,
		2014		2013
	Accounts payable	$	99,508	$	61,936
	Accrued payroll and related costs	92,778		69,429
	Accrued clinical trial expense	41,555		23,654
	Accrued sales-related charges, deductions, and royalties	133,085		66,855
	Other accrued expenses and liabilities	117,302		29,022
		$	484,228	$	250,896

Deferred_Revenue_Tables

Deferred Revenue (Tables)	12 Months Ended
	Dec. 31, 2014
Deferred Revenue Disclosure [Abstract]
Deferred Revenue, by Arrangement, Disclosure	Deferred revenue consists of the following:
		As of December 31,
		2014		2013
	Current portion:
	Received or receivable from Sanofi (see Note 4a)	$	15,927	$	12,815
	Received or receivable from Bayer HealthCare (see Note 4b)	33,652		9,738
	Received for technology license agreement (see Note 5)	23,572		23,572
	Other	874		875
		$	74,025	$	47,000
	Long-term portion:
	Received or receivable from Sanofi (see Note 4a)	$	72,367	$	76,522
	Received or receivable from Bayer HealthCare (see Note 4b)	46,486		26,683
	Received for technology license agreement (see Note 5)	57,423		80,994
		$	176,276	$	184,199

Convertible_Debt_Tables

Convertible Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The net carrying amount of the liability component of the Notes consists of the following:
		As of December 31,
		2014			2013
	Total convertible senior notes - par	$	169,400		$	400,000
	Unamortized discount	(22,627		)	(79,685		)
		$	146,773		$	320,315
Interest Expense Associated with Convertible Notes
		Year Ended December 31,
		2014			2013			2012
	Contractual coupon interest rate	$	5,036		$	7,230		$	7,503
	Amortization of discount and note issuance costs	17,821			22,980			21,623
		$	22,857		$	30,210		$	29,126

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments Under Operating Leases	The estimated future minimum noncancelable lease commitments under operating leases, as of December 31, 2014, are as follows:
		Facilities		Equipment		Total
	2015	$	9,370	$	1,449	$	10,819
	2016	10,040		151		10,191
	2017	9,592		13		9,605
	2018	9,779		—		9,779
	2019	9,957		—		9,957
	Thereafter	58,271		—		58,271
		$	107,009	$	1,613	$	108,622
Rent Expense Under Operating Leases	Rent expense under operating leases was:
	Year Ended December 31,	Facilities		Equipment		Total
	2014	$	13,360	$	952	$	14,312
	2013	9,404		471		9,875
	2012	7,428		601		8,029
Commitments Under Facility Lease Obligations	The estimated future minimum noncancelable commitments under these facility lease obligations, as of December 31, 2014, are as follows:
		Buildings A and B		Building C		Total
	2015	$	13,545	$	4,562	$	18,107
	2016	13,809		4,688		18,497
	2017	14,079		4,818		18,897
	2018	14,356		4,951		19,307
	2019	14,640		5,088		19,728
	Thereafter	132,027		59,987		192,014
		$	202,456	$	84,094	$	286,550

LongTerm_Incentive_Plans_Table

Long-Term Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Transactions Involving Stock Option Awards	Transactions involving stock option awards during 2014 under the Company's Incentive Plans are summarized in the table below.
	Stock Options:			Number of Shares			Weighted-Average Exercise Price				Weighted-Average Remaining Contractual Term (in years)	Intrinsic Value (in thousands)
	Outstanding as of December 31, 2013			21,408,268			$	98.1
	2014:00:00	Granted		3,913,368			$	385.33
		Forfeited		(252,126	)		$	155.37
		Expired		(350	)		$	64.35
		Exercised		(3,562,900	)		$	44.72
	Outstanding as of December 31, 2014			21,506,260			$	158.54			6.99	$	5,467,783
	Vested and expected to vest as of December 31, 2014			20,988,044			$	154.81			6.94	$	5,414,258
	Exercisable as of December 31, 2014			12,104,560			$	65.48			5.53	$	4,203,941
Weighted-Average Exercise Prices and Weighted-Average Grant-Date Fair Values of Options Issued	The fair value of each option granted under the Company's Incentive Plans during 2014, 2013, and 2012 was estimated on the date of grant using the Black-Scholes option-pricing model.
			Number of Options Granted			Weighted-Average Exercise Price				Weighted-Average Fair Value
	2014:00:00
	Exercise price equal to Market Price		3,913,368			$	385.33			$	140.38
	2013:00:00
	Exercise price equal to Market Price		3,937,989			$	263.77			$	104.9
	2012:00:00
	Exercise price equal to Market Price		4,162,653			$	167.96			$	67.66
Weighted-Average Values of Assumptions Used in Computing Fair Value of Option Grants	The following table summarizes the weighted average values of the assumptions used in computing the fair value of option grants during 2014, 2013 and 2012.
			2014			2013			2012
	Expected volatility		39	%		42	%		45	%
	Expected lives from grant date		5.2 years			5.3 years			5.4 years
	Expected dividend yield		0	%		0	%		0	%
	Risk-free interest rate		1.62	%		1.73	%		0.86	%
Activity Related to Restricted Stock Awards	A summary of the Company's activity related to Restricted Stock awards for the year ended December 31, 2014 is summarized below:
	Restricted Stock:			Number of Shares			Weighted-Average Grant Date Fair Value
	Outstanding as of December 31, 2013			538,580			$	112.16
	2014:00:00	Granted		7,500			$	338.32
		Vested		(20	)		$	237.68
	Outstanding as of December 31, 2014			546,060			$	115.26

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	Components of income before income taxes consist of the following (foreign income before income taxes in 2012 was not material):
			Year Ended December 31,
			2014				2013
	United States		$	1,115,958			$	812,278
	Foreign		(340,211		)		(98,918		)
			$	775,747			$	713,360
Schedule of Components of Income Tax Expense (Benefit)	Components of income tax expense (benefit) consist of the following:
			Year Ended December 31,
			2014				2013			2012
	Current:
		Federal	$	447,370			$	201,475		—
		State	28,718				23,489			$	4,308
		Foreign	2,879				433			—
		Total current tax expense (benefit)	478,967				225,397			4,308
	Deferred:
		Federal	(68,700		)		54,910			(300,319		)
		State	18,891				8,700			(39,837		)
		Foreign	(1,485		)		(9		)	—
		Total deferred tax expense (benefit)	(51,294		)		63,601			(340,156		)
			$	427,673			$	288,998		$	(335,848	)
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the U.S. statutory income tax rate to the Company's effective income tax rate is as follows:
		Year Ended December 31,
		2014			2013			2012
	U.S. federal statutory tax rate	35	%		35	%		35	%
	State and local income taxes	2			3.4			5.4
	Change in state effective rate	2.8			—			5.4
	Foreign income tax rate differential	15.3			4.9			—
	Income tax credits	(7.4	)		(4.9	)		—
	Reclassification of net operating losses related to exercises of stock options	—			—			9.3
	Provision (benefit) attributable to valuation allowances	—			—			(139.0	)
	Provision (benefit) related to uncertain tax positions	2.5			—			—
	Non-deductible Branded Prescription Drug Fee	2.7			1.1			—
	Other permanent differences	2.2			1			2.8
	Effective income tax rate	55.1	%		40.5	%		(81.1	)%
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company's deferred tax assets and liabilities are as follows:
			As of December 31,
			2014				2013
	Deferred tax assets:
	Net operating loss carry-forward		$	150			$	135
	Fixed assets		8,078				18,902
	Deferred revenue		75,503				88,033
	Deferred compensation		194,489				109,715
	Income tax credit carry-forwards		16,099				9,372
	Capitalized research and development costs		12,908				18,942
	Other		41,252				34,215
			348,479				279,314
	Valuation allowance		(359		)		(1,830		)
	Total deferred tax assets		348,120				277,484
	Deferred tax liabilities:
	Unrealized gains/losses on marketable securities		(28,186		)		—
	Convertible senior notes		(252		)		(929		)
	Other		(3,578		)		—
			(32,016		)		(929		)
	Net deferred tax assets		$	316,104			$	276,555
Schedule Of Unrecognized Tax Benefits Roll Forward	The following table summarizes the gross amounts of unrecognized tax benefits, without regard to reduction in tax liabilities or additions to deferred tax assets and liabilities if such unrecognized tax benefits were settled. The amount, if recognized, that would impact the effective tax rate is $51.2 million, $23.5 million, and $8.4 million as of December 31, 2014, 2013, and 2012, respectively.
			2014				2013			2012
	Balance as of January 1		$	26,627			$	11,274		$	5,596
	Gross increases related to current year tax positions		27,538				7,620			1,873
	Gross increases related to prior year tax positions		6,464				8,305			3,805
	Gross decrease due to settlements, recapture, filed returns, and lapse of statutes of limitation		(3,014		)		(572		)	—
	Balance as of December 31		$	57,615			$	26,627		$	11,274

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
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:
		December 31,
		2014			2013			2012
	Net income - basic	$	348,074		$	424,362		$	750,269
	Effect of dilutive securities:
	Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs	—			—			29,126
	Net income - diluted	$	348,074		$	424,362		$	779,395
	(Shares in thousands)
	Weighted average shares - basic	100,612			97,917			94,685
	Effect of dilutive securities:
	Stock options	9,440			10,233			14,231
	Restricted stock	425			433			715
	Convertible senior notes	—			—			4,761
	Warrants	2,936			2,707			990
	Dilutive potential shares	12,801			13,373			20,697
	Weighted average shares - diluted	113,413			111,290			115,382
	Net income per share - basic	$	3.46		$	4.33		$	7.92
	Net income per share - diluted	$	3.07		$	3.81		$	6.75
Antidilutive Securities	Shares which have been excluded from the December 31, 2014, 2013, and 2012 diluted per share amounts because their effect would have been antidilutive, include the following:
		December 31,
	(Shares in thousands)	2014		2013			2012
	Stock options	1,470		304			325
	Convertible senior notes	4,247		4,761			—

Unaudited_Quarterly_Results_Ta

Unaudited Quarterly Results (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2014 and 2013 are set forth in the following tables.
		First Quarter Ended		Second Quarter Ended		Third Quarter Ended		Fourth Quarter Ended
		31-Mar-14		30-Jun-14		30-Sep-14		31-Dec-14
		(Unaudited)
	Revenues (1)	$	625,740	$	665,700	$	725,788	$	802,329
	Net income (2)	$	65,443	$	92,735	$	79,720	$	110,176
	Net income per share - basic	$	0.66	$	0.92	$	0.79	$	1.09
	Net income per share - diluted	$	0.58	$	0.82	$	0.7	$	0.96
		First Quarter Ended		Second Quarter Ended		Third Quarter Ended		Fourth Quarter Ended
		31-Mar-13		30-Jun-13		30-Sep-13		31-Dec-13
		(Unaudited)
	Revenues (3)	$	439,664	$	457,642	$	597,027	$	610,412
	Net income	$	98,874	$	87,376	$	141,306	$	96,806
	Net income per share - basic	$	1.02	$	0.89	$	1.44	$	0.98
	Net income per share - diluted	$	0.9	$	0.79	$	1.25	$	0.86
	(1) Revenues in the first, second, third, and fourth quarters of 2014 included recognition of sales milestones of $30.0 million, $15.0 million, $30.0 million, and $30.0 million, respectively.
	(2) Net income in the third quarter of 2014 included a $40.6 million incremental charge related to the Branded Prescription Drug Fee based on final regulations issued by the IRS in July 2014 as described in Note 3 above.
	(3) Revenues in the second quarter of 2013 were reduced by two $10 million up-front payments made to Sanofi to acquire full rights to antibodies to PDGF and antibodies to Ang2 in ophthalmology, as described in Note 4 above. Revenues in the third and fourth quarter of 2013 included recognition of sales and substantive development milestones of $45.0 million and $25.0 million, respectively.

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue Recognition [Abstract]
Percentage of prompt pay discount the company accrues	100.00%
Concentration Risks, Types, No Concentration Percentage [Abstract]
Allowance for Doubtful Accounts Receivable, Current	$0	$0
Provision for Doubtful Accounts	$0	$0	$0
Building and improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Building and improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Laboratory and other equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Laboratory and other equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Furniture and Fixtures [Member] | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years

Net_Product_Sales_Details

Net Product Sales (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue Disclosure [Line Items]
Branded Prescription Drug Fee	$40,600,000
Net product sales	1,750,762,000	1,425,839,000	858,093,000
Activity of Sales Related Deductions [Roll Forward]
Balance	24,781,000	24,601,000	18,826,000	2,218,000
Provision related to current period sales	111,855,000	89,875,000	62,251,000
Credits/payments	-111,675,000	-84,100,000	-45,643,000
Rebates and Chargebacks
Activity of Sales Related Deductions [Roll Forward]
Balance	3,083,000	4,400,000	2,983,000	585,000
Provision related to current period sales	33,117,000	25,936,000	14,153,000
Credits/payments	-34,434,000	-24,519,000	-11,755,000
Distribution Related Fees
Activity of Sales Related Deductions [Roll Forward]
Balance	21,166,000	19,663,000	15,298,000	1,451,000
Provision related to current period sales	77,160,000	62,984,000	45,028,000
Credits/payments	-75,657,000	-58,619,000	-31,181,000
Other Sales Related Deductions
Activity of Sales Related Deductions [Roll Forward]
Balance	532,000	538,000	545,000	182,000
Provision related to current period sales	1,578,000	955,000	3,070,000
Credits/payments	-1,584,000	-962,000	-2,707,000
Customer concentration risk | Gross Sales Revenue
Risks and Uncertainties [Abstract]
Concentration risk, percentage	73.00%	76.00%	78.00%
EYLEA
Revenue Disclosure [Line Items]
Net product sales	1,736,400,000	1,408,700,000	837,900,000
ARCALYST
Revenue Disclosure [Line Items]
Net product sales	$14,400,000	$17,100,000	$20,200,000

Collaboration_Agreements_Sanof

Collaboration Agreements (Sanofi) (Details) (USD $)	3 Months Ended						12 Months Ended			1 Months Ended		3 Months Ended	11 Months Ended	1 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 31, 2014	Nov. 30, 2007	Jun. 30, 2013	Nov. 30, 2009	Jan. 31, 2006	Jan. 31, 2005	Sep. 30, 2003
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized	$30,000,000	$30,000,000	$15,000,000	$30,000,000	$25,000,000	$45,000,000
Research and Development Expense							1,271,353,000	859,947,000	625,554,000
Revenue from Related Parties							541,299,000	430,111,000	423,814,000
Number of therapeutic antibodies currently under development							5
Period for Achieving Sales Target for Milestone Payment, Rolling Basis							12 months
Collaboration Agreement with Sanofi
Collaboration Agreements [Line Items]
Common Stock, shares issued (in shares)	22,859,144						22,859,144
Antibody Collaboration
Collaboration Agreements [Line Items]
Contingent reimbursement obligation	1,304,000,000						1,304,000,000
Recognition of Deferred Revenue							10,243,000	10,243,000	10,233,000
Net profit (loss) from commercialization of products under collaboration agreement							-41,378,000	0	0
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned							547,761,000	453,489,000	365,245,000
Contracts Revenue							19,480,000	1,868,000	0
Research and Development Asset Acquired Other than Through Business Combination, Written-off							0	-20,000,000	0
Due from Related Parties, Current	110,600,000				106,100,000		110,600,000	106,100,000
Research and Development Expense							109,700,000	17,600,000
Deferred Revenue	64,400,000				71,200,000		64,400,000	71,200,000
Revenue from Related Parties							536,106,000	445,600,000	375,478,000
Proceeds from Collaborators											85,000,000
Percentage of repayment of development balance out of profits							50.00%
Minimum advance notice required to terminate collaboration agreement							3 months
Annual funding maximum of research activities per amended agreement													160,000,000
Additional years to extend the agreement													3 years
Substantive milestone payment to the Company							10,000,000
Percentage of Trial Costs borne by collaborating party							80.00%
Percentage of Trial Costs borne by entity							20.00%
Percentage of trial costs to be reimbursed due to profitability of agreement							30.00%
Excess Share of profit not required to to be applied to reimburse development cost							10.00%
Starting share of profits outside the United States, based on sales, for collaborating party							65.00%
Starting share of profits outside the United States, based on sales, for Company							35.00%
Ending share of profits outside the United States, based on sales, for collaborating party							55.00%
Ending share of profits outside the United States, based on sales, for Company							45.00%
Share of losses outside the United States, for collaborating party							55.00%
Share of losses outside the United States, for Company							45.00%
Maximum amount of sales milestone payments if total sales achieve specific levels							250,000,000
Starting specified levels of annual sales at which sales milestone payments may be received							1,000,000,000
Period for Achieving Sales Target for Milestone Payment, Rolling Basis							12 months
Amount of funding of agreed-upon cost incurred to expand manufacturing capacity							30,000,000
Maximum amount of reimbursement related to capital expenditures							17,500,000
Period of Notice to Opt Out of Further Development and or Commercialization							12 months
Period of Notice to Opt Out of Further Development Upon Entering of Joint Development Product							30 days
Number of families of novel antibodies								2				2
Payments for Purchase of Other Assets										67,500,000
Sanofi
Collaboration Agreements [Line Items]
Research and Development Asset Acquired Other than Through Business Combination, Written-off		-33,800,000
VelociGene Agreement
Collaboration Agreements [Line Items]
Minimum payment received under the agreement	21,500,000						21,500,000
PDGF
Collaboration Agreements [Line Items]
Research and Development Asset Acquired Other than Through Business Combination, Written-off												-10,000,000
Number of Payments the Company made							2
Other Research and Development Expense							5,000,000
Potential future milestone payments							30,000,000
Ang2
Collaboration Agreements [Line Items]
Research and Development Asset Acquired Other than Through Business Combination, Written-off												-10,000,000
ZALTRAP Agreement
Collaboration Agreements [Line Items]
Contingent reimbursement obligation	461,000,000						461,000,000
Net profit (loss) from commercialization of products under collaboration agreement							-4,715,000	-30,810,000	-25,634,000
Revenue Recognition, Milestone Method, Revenue Recognized							0	0	50,000,000
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned							4,806,000	5,639,000	10,702,000
Contracts Revenue							5,102,000	9,682,000	13,268,000
Due from Related Parties, Current	10,500,000						10,500,000
Due to Related Parties, Current					1,400,000			1,400,000
Deferred Revenue	23,900,000				18,200,000		23,900,000	18,200,000
Revenue from Related Parties							5,193,000	-15,489,000	48,336,000
Proceeds from Collaborators														25,000,000	25,000,000	80,000,000
Number of shares of Common Stock purchased																2,799,552
Cash price of newly issued, unregistered shares of Common Stock purchased																45,000,000
Revenue based on percentage of annual sales in Japan							35.00%
Amount of milestone payments that may be received relating to marketing approval							350,000,000
Percentage of repayment of development balance out of profits							50.00%
Amount of non refundable payment received for collaboration agreement															$25,000,000
Minimum advance notice required to terminate collaboration agreement							12 months
Percentage of development expenses to be reimbursed due to termination of collaboration agreement							50.00%

Collaboration_Agreements_Bayer

Collaboration Agreements (Bayer HealthCare LLC) (Details) (USD $)	3 Months Ended						12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized	$30,000,000	$30,000,000	$15,000,000	$30,000,000	$25,000,000	$45,000,000
Other Collaboration Revenue							495,555,000	220,289,000	70,099,000
Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreement [Abstract]
Contingent reimbursement obligation	263,000,000						263,000,000
Collaboration Agreements [Line Items]
Royalty rate minimum							33.50%
Royalty rate maximum							40.00%
Net profit (loss) from commercialization of products under collaboration agreement							301,302,000	101,494,000	0
Revenue Recognition, Milestone Method, Revenue Recognized							105,000,000	70,000,000	25,000,000
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned							23,383,000	20,905,000	34,892,000
Contracts Revenue							52,390,000	27,890,000	10,207,000
Other Collaboration Revenue							482,075,000	220,289,000	70,099,000
PDGFR-beta outside the US
Collaboration Agreements [Line Items]
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned							2,848,000	0	0
Contracts Revenue							10,632,000	0	0
Other Collaboration Revenue							13,480,000	0	0
sales achievement - 1 billion [Member]
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - $900 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - $600 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							$15,000,000

Collaboration_Agreements_EYLEA

Collaboration Agreements (EYLEA) (Details) (USD $)	3 Months Ended						12 Months Ended	1 Months Ended		12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2014	Aug. 31, 2007	Oct. 31, 2006	Dec. 31, 2013	Dec. 31, 2012
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized	$30,000,000	$30,000,000	$15,000,000	$30,000,000	$25,000,000	$45,000,000
Number of sales milestone payments the Company received							6
Period for Achieving Sales Target for Milestone Payment, Rolling Basis							12 months
levels of twelve month sales at which sales milestone payments maybe received - 200 million							200,000,000
Levels of twelve month sales at which sales milestone payments were received							500,000,000
Levels of twelve month sales at which sales milestone payments were received - 600 million							600,000,000
Levels of twelve month sales at which sales milestone payments were received - 700 million							700,000,000
Levels of twelve month sales at which sales milestone payments were received - 800 million		800,000,000
Levels of twelve month sales at which sales milestone payments were received - 900 million		900,000,000
levels of twelve months sales at which sales milestone payments maybe received - 1 billion	1,000,000,000
level of twelve months sales at which sales milestone payments maybe received - 100 million							100,000,000
Accounts receivable from Bayer HealthCare	156,962,000				63,189,000		156,962,000			63,189,000
Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Percentage of repayment of development balance out of profits							50.00%
Contingent reimbursement obligation	263,000,000						263,000,000
Revenue Recognition, Milestone Method, Revenue Recognized							105,000,000			70,000,000	25,000,000
Number of sales milestone payments the Company received										3
Period for Achieving Sales Target for Milestone Payment, Rolling Basis										12 months
Number of sales milestone payments the Company might receive							1
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned							23,383,000			20,905,000	34,892,000
Proceeds from Collaborators								20,000,000	75,000,000
Other Research and Development Expense							18,600,000			15,300,000	21,900,000
Accounts receivable from Bayer HealthCare	155,800,000				63,200,000		155,800,000			63,200,000
Deferred Revenue	60,200,000				36,400,000		60,200,000			36,400,000
BRVO
Collaboration Agreements [Line Items]
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned				15,700,000
sales achievement - 1 billion [Member]
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
Marketing Approval | Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized										15,000,000	15,000,000
Pricing Approval | Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized										10,000,000	10,000,000
sales achievement - $200 million
Collaboration Agreements [Line Items]
Period for Achieving Sales Target for Milestone Payment, Rolling Basis							12 months
sales achievement - $200 million | Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized										15,000,000
Starting specified levels of annual sales at which sales milestone payments maybe received -1st tier										200,000,000
sales achievement - $300 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized										15,000,000
sales achievement - $300 million | Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Starting specified levels of annual sales at which sales milestone payments maybe received - 2nd tier										300,000,000
sales achievement - $400 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized										15,000,000
sales achievement - $400 million | Collaboration Agreement with Bayer HealthCare LLC
Collaboration Agreements [Line Items]
Starting specified levels of annual sales at which sales milestone payments may be received - 3rd tier										400,000,000
sales achievement - $500 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - $600 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - 700 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - $800 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - $900 million
Collaboration Agreements [Line Items]
Revenue Recognition, Milestone Method, Revenue Recognized							15,000,000
sales achievement - 200 million
Collaboration Agreements [Line Items]
Maximum amount of sales milestone payments if total sales achieve specific levels							15,000,000
sales achievement - 100 million
Collaboration Agreements [Line Items]
Period for Achieving Sales Target for Milestone Payment, Rolling Basis							12 months
Maximum amount of sales milestone payments if total sales achieve specific levels							$15,000,000

Collaboration_Agreements_PDGFR

Collaboration Agreements (PDGFR-beta Antibody) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2014
Collaboration Agreements [Line Items]
Accounts receivable from Bayer HealthCare		$156,962,000	$63,189,000
PDGFR-beta outside the US
Collaboration Agreements [Line Items]
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions		20.00%		20.00%
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%
Percentage of development milestone payments to be reimbursed		0.00%
Number of development milestone payments the Company received	2
Deferred Revenue, Additions	2,500,000
Future development milestone payment		15,000,000
Opt in payment		20,000,000
Amount of milestone payment that may be received relating to marketing approval		20,000,000
Accounts receivable from Bayer HealthCare		1,200,000
Deferred Revenue		19,900,000
Proceeds from Collaborators		$25,500,000

Collaboration_Agreements_Avala

Collaboration Agreements (Avalanche Biotechnologies, Inc.) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Collaboration Agreements [Line Items]
Payments to Acquire Marketable Securities	$564,188,000	$577,278,000	$470,945,000
Collaboration Agreement, Avalanche Biotechnologies, Inc
Collaboration Agreements [Line Items]
Research and Development Asset Acquired Other than Through Business Combination, Written-off	2,000,000
Pre-payment of collaboration research costs	6,000,000
Potential future milestone payments	640,000,000
Number of therapeutic targets	8
Payment to acquire preferred share of non-public entity	5,000,000
Number of therapeutic targets of Avalanche's choice	2
Payments to Acquire Marketable Securities	10,000,000
Number of Shares of Common Stock had purchased	588,235
Product | Collaboration Agreement, Avalanche Biotechnologies, Inc
Collaboration Agreements [Line Items]
Potential future milestone payments	$80,000,000

Technology_Licensing_Agreement1

Technology Licensing Agreements (Details) (USD $)	1 Months Ended		12 Months Ended
	Aug. 31, 2010	Mar. 31, 2007	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Revenue Arrangement [Line Items]
Technology licensing revenue			$31,941,000	$28,506,000	$26,471,000
License Agreement with Astellas Pharma Inc.
Deferred Revenue Arrangement [Line Items]
Non-exclusive license agreement term		6 years
Advance payment received due to amended licensing agreement	165,000,000
Recognition period for advance payment	7 years
Future payment to be made under terms of amended licensing agreement			130,000,000
Number of days of advance written notice to terminate agreement			90 days
Technology licensing revenue			23,600,000	23,600,000	23,600,000
Deferred Revenue			$81,000,000	$104,600,000

Marketable_Securities_Details

Marketable Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	$1,200,000	$1,000,000
Amortized Cost Basis	631,477,000	548,322,000
Unrealized Gains	81,989,000	392,000
Unrealized (Losses)	-1,551,000	-447,000
Total fair value of available-for-sale marketable securities	711,915,000	548,267,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Maturities within one year	251,761,000	158,376,000
Maturities after one year through five years	360,208,000	383,410,000
Maturities after five years through ten years	1,128,000	4,138,000
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	0	1,177,000
Total	613,097,000	547,101,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	426,941,000	239,812,000
Fair Value - 12 Months or Greater	0	0
Fair Value - Total	426,941,000	239,812,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	-1,551,000	-447,000
Unrealized Loss - 12 Months or Greater	0	0
Unrealized Loss - Total	-1,551,000	-447,000
Available-for-sale Securities, Gross Realized Losses	0	0
Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	616,477,000	548,322,000
Unrealized Gains	5,550,000	392,000
Unrealized (Losses)	-1,551,000	-447,000
Total fair value of available-for-sale marketable securities	620,476,000	548,267,000
U.S. government and government agency obligations
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	25,549,000	49,241,000
Fair Value - Total	25,549,000	49,241,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	-46,000	-27,000
Unrealized Loss - Total	-46,000	-27,000
U.S. government and government agency obligations | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	28,596,000	107,493,000
Unrealized Gains	3,000	55,000
Unrealized (Losses)	-46,000	-27,000
Total fair value of available-for-sale marketable securities	28,553,000	107,521,000
Corporate bonds
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	390,613,000	176,140,000
Fair Value - Total	390,613,000	176,140,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	-1,462,000	-361,000
Unrealized Loss - Total	-1,462,000	-361,000
Corporate bonds | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	548,832,000	369,321,000
Unrealized Gains	136,000	233,000
Unrealized (Losses)	-1,462,000	-361,000
Total fair value of available-for-sale marketable securities	547,506,000	369,193,000
Commercial Paper | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		23,891,000
Unrealized Gains		53,000
Unrealized (Losses)		0
Total fair value of available-for-sale marketable securities		23,944,000
International government agency obligations | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		2,007,000
Unrealized Gains		1,000
Unrealized (Losses)		0
Total fair value of available-for-sale marketable securities		2,008,000
Certificates of Deposit | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		7,509,000
Unrealized Gains		5,000
Unrealized (Losses)		0
Total fair value of available-for-sale marketable securities		7,514,000
Municipal Bonds [Member]
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	10,779,000	14,431,000
Fair Value - Total	10,779,000	14,431,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	-43,000	-59,000
Unrealized Loss - Total	-43,000	-59,000
Municipal Bonds [Member] | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	37,044,000	36,935,000
Unrealized Gains	37,000	45,000
Unrealized (Losses)	-43,000	-59,000
Total fair value of available-for-sale marketable securities	37,038,000	36,921,000
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments	0	2,900,000	0
Equity Securities [Member] | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	2,005,000	1,166,000
Unrealized Gains	5,374,000	0
Unrealized (Losses)	0	0
Total fair value of available-for-sale marketable securities	7,379,000	1,166,000
Equity Securities [Member] | Restricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	15,000,000
Unrealized Gains	76,439,000
Unrealized (Losses)	0
Total fair value of available-for-sale marketable securities	$91,439,000

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2011
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	$711,915,000	$548,267,000
Convertible Debt [Abstract]
Total convertible senior notes - par		400,000,000
Liabilities, Current	654,660,000	298,835,000
Convertible senior notes
Convertible Debt [Abstract]
Total convertible senior notes - par	169,400,000	400,000,000		400,000,000
Interest rate, stated percentage	1.88%	1.88%		1.88%
Fair value of the outstanding notes	819,800,000	1,327,200,000
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other than Temporary Impairment Losses, Investments	0	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of marketable securities held			1
Available-for-sale marketable securities:
Marketable Securities, Unrealized Gain (Loss)	0	0
Unrestricted
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	620,476,000	548,267,000
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	7,379,000	1,166,000
Measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	704,536,000	547,101,000
Measured on a recurring basis | Unrestricted | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	7,379,000	1,166,000
Total fair value of available-for-sale marketable securities	7,379,000
Measured on a recurring basis | Unrestricted | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
U.S. government and government agency obligations	28,553,000	107,521,000
Commercial Paper, at Carrying Value		23,944,000
Municipal Debt Securities, at Carrying Value	37,038,000	36,921,000
Available-for-sale Securities, Equity Securities	547,506,000	369,193,000
International Government Obligations Fair Value Disclosure		2,008,000
Certificates of Deposit, at Carrying Value		7,514,000
Total fair value of available-for-sale marketable securities	613,097,000
Measured on a recurring basis | Restricted | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	91,439,000
Fair Value | Measured on a recurring basis
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	711,915,000	548,267,000
Fair Value | Measured on a recurring basis | Unrestricted
Available-for-sale marketable securities:
U.S. government and government agency obligations	28,553,000	107,521,000
Financial Instruments, Owned, Corporate Debt, at Fair Value	547,506,000	369,193,000
Commercial Paper, at Carrying Value		23,944,000
Municipal Debt Securities, at Carrying Value	37,038,000	36,921,000
Available-for-sale Securities, Equity Securities	7,379,000	1,166,000
International Government Obligations Fair Value Disclosure		2,008,000
Certificates of Deposit, at Carrying Value		7,514,000
Total fair value of available-for-sale marketable securities	620,476,000
Fair Value | Measured on a recurring basis | Restricted
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	91,439,000
Warrant Transactions
Convertible Debt [Abstract]
Other Liabilities, Fair Value Disclosure	$87,500,000

Inventory_Details

Inventory (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]
Raw materials	$10,923,000	$9,120,000
Work in process	73,519,000	35,868,000
Finished goods	10,768,000	14,352,000
Deferred costs	33,651,000	11,014,000
Total Inventories	128,861,000	70,354,000
Inventory write-downs and reserves	$6,000,000	$9,100,000	$17,000,000

Property_Plant_and_Equipment_D

Property, Plant, and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Land	$2,768,000	$2,768,000
Buildings and Improvements, Gross	398,981,000	343,363,000
Leasehold Improvements, Gross	42,600,000	26,370,000
Construction in Progress, Gross	472,231,000	142,370,000
Property, plant, and equipment, gross	1,228,293,000	748,600,000
Furniture and Fixtures, Gross	58,655,000	44,186,000
Less: accumulated depreciation and amortization	-253,984,000	-221,617,000
Property, plant, and equipment, net	974,309,000	526,983,000
Depreciation and amortization expense	52,686,000	41,204,000	36,940,000
New Laboratory and Office Facilities [Member]
Property, Plant and Equipment [Line Items]
Costs incurred by the landlord to construct new laboratory and office facilities	236,700,000	111,100,000
Laboratory and other equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	253,058,000	189,543,000
UNITED STATES
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	754,700,000	503,500,000
Foreign
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	$219,600,000	$23,500,000

Accounts_Payable_and_Accrued_E2

Accounts Payable and Accrued Expenses (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accounts payable	$99,508,000	$61,936,000
Accrued payroll and related costs	92,778,000	69,429,000
Accrued clinical trial expense	41,555,000	23,654,000
Accrued sales-related charges, deductions and royalties	133,085,000	66,855,000
Other accrued expenses and liabilities	117,302,000	29,022,000
Accounts payable and accrued expenses	484,228,000	250,896,000
Warrant Transactions
Payables and Accruals [Abstract]
Accounts Payable, Other	$59,800,000

Deferred_Revenue_Details

Deferred Revenue (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current portion:
Deferred revenue, current portion	$74,025	$47,000
Long-term portion:
Deferred revenue, long-term portion	176,276	184,199
Received or receivable from Sanofi
Current portion:
Deferred revenue, current portion	15,927	12,815
Long-term portion:
Deferred revenue, long-term portion	72,367	76,522
Received or receivable from Bayer HealthCare
Current portion:
Deferred revenue, current portion	33,652	9,738
Long-term portion:
Deferred revenue, long-term portion	46,486	26,683
Received for technology license agreement
Current portion:
Deferred revenue, current portion	23,572	23,572
Long-term portion:
Deferred revenue, long-term portion	57,423	80,994
Other
Current portion:
Deferred revenue, current portion	$874	$875

Convertible_Debt_Details

Convertible Debt (Details) (USD $)	1 Months Ended		12 Months Ended			3 Months Ended
	Nov. 30, 2014	Oct. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015	Jan. 31, 2015
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par				$400,000,000
Convertible Notes Payable, Noncurrent			146,773,000	320,315,000
Treasury Stock, Shares			2,017,732	0
Warrants [Abstract]
Proceeds received from the Warrant		93,800,000
Repayments of Convertible Debt			220,639,000	0	0
Loss on Extinguishment of Debt			33,469,000	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Payments for Repurchase of Warrants			294,552,000	0	0
Maximum number of shares issuable upon exercise of warrants			3,540,095	4,760,840
Maximum reduction of warrants held by warrant holder	493,229
Fair Value Adjustment of Warrants			1,200,000
Maximum amount of warrant payable			-148,496,000
Maximum share price for warrant holders to close out hedge position	$397.75
Convertible Debt [Abstract]
Debt Conversion			230,600,000
Warrant Transactions
Warrants [Abstract]
Strike price of the warrant transaction (in dollars per share)		103.41
Proceeds received from the Warrant		93,800,000
Accounts Payable, Other			59,800,000
Reduction of warrant numbers			202,560
Liabilities, Fair Value Adjustment			87,500,000
Call option
Convertible Debt [Abstract]
Purchase of convertible note hedges		117,500,000
Debt Instrument, Redemption, Criteria One [Member]
Debt Instrument [Line Items]
Number of trading days			20
Number of consecutive trading days			30 days
Percentage of stock price trigger			130.00%
Debt Instrument, Redemption, Criteria Two [Member]
Debt Instrument [Line Items]
Number of trading days			5
Number of consecutive trading days			10 days
Percentage of stock price trigger			98.00%
Debt Instrument, Redemption, Criteria Three [Member]
Debt Instrument [Line Items]
Calendar day period after the record date of equity instruments issuance			60 days
Number of consecutive days			10 days
Convertible senior notes
Debt Instrument [Line Items]
Interest rate, stated percentage		1.88%	1.88%	1.88%
Initial conversion ratio		11.9021
Increment of principal amount for conversion		1,000
Total shares upon conversion (in shares)		4,760,840
Initial conversion price (in dollars per share)		$84.02
Percentage of principal value that holders can require Company to repurchase		100.00%
Estimated fair value of the liability component		271,100,000
Carrying amount of equity component		120,900,000
Gross proceeds from the issuance of the Notes		392,000,000
Effective interest rate used to amortize the discount on the liability component			10.20%
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par		400,000,000	169,400,000	400,000,000
Unamortized discount			-22,627,000	-79,685,000
Convertible Notes Payable, Noncurrent			146,773,000	320,315,000
Interest Expense, Debt [Abstract]
Contractual coupon interest rate			5,036,000	7,230,000	7,503,000
Amortization of discount and note issuance costs			17,821,000	22,980,000	21,623,000
Total interest expense			22,857,000	30,210,000	29,126,000
Warrants [Abstract]
Trading days to calculate settlement			40
Convertible Debt [Abstract]
If-converted value in excess of principal			691,600,000
Additional Paid-in Capital
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Maximum amount of warrant payable			-148,496,000
Scenario, Forecast [Member]
Convertible Debt [Abstract]
Debt Conversion						6,700,000
Subsequent Event [Member] | Warrant Transactions
Warrants [Abstract]
Accounts Payable, Other							$62,000,000
Reduction of warrant numbers						206,480

Commitments_and_Contingencies_1

Commitments and Contingencies - Operating Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments under operating leases [Abstract]
2015	$10,819,000
2016	10,191,000
2017	9,605,000
2018	9,779,000
2019	9,957,000
Thereafter	58,271,000
Total	108,622,000
Rent expense under operating leases [Abstract]
Rent expense under operating leases	14,312,000	9,875,000	8,029,000
Rent charges for utilities, real estate taxes, and operating expense	13,600,000	11,500,000	10,900,000
Facilities
Commitments under operating leases [Abstract]
2015	9,370,000
2016	10,040,000
2017	9,592,000
2018	9,779,000
2019	9,957,000
Thereafter	58,271,000
Total	107,009,000
Rent expense under operating leases [Abstract]
Rent expense under operating leases	13,360,000	9,404,000	7,428,000
Equipment
Commitments under operating leases [Abstract]
2015	1,449,000
2016	151,000
2017	13,000
2018	0
2019	0
Thereafter	0
Total	1,613,000
Rent expense under operating leases [Abstract]
Rent expense under operating leases	$952,000	$471,000	$601,000
Facilities - Buildings A and B and C
Operating Leases [Abstract]
Number of new buildings leased	2
Number of renewal options to extend the term of the lease	3
Lease renewal escalation percentage	2.50%
Tarrytown lease [Abstract]
Lease extension terms	5 years
Facilities Building D and E
Operating Leases [Abstract]
Number of renewal options to extend the term of the lease	3
Number of new buildings to be constructed	2
Tarrytown lease [Abstract]
Initial term of lease	15 years
Lease extension terms	5 years

Commitments_and_Contingencies_2

Commitments and Contingencies - Facility Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Facility Leases [Line Items]
2015	$18,107,000
2016	18,497,000
2017	18,897,000
2018	19,307,000
2019	19,728,000
Thereafter	192,014,000
Total	286,550,000
Facility lease obligations [Abstract]
Interest expense in connection with facility lease obligation	14,500,000	16,200,000	16,000,000
Facilities - Buildings A and B and C
Schedule of Facility Leases [Line Items]
2015	13,545,000
2016	13,809,000
2017	14,079,000
2018	14,356,000
2019	14,640,000
Thereafter	132,027,000
Total	202,456,000
Facility lease obligations [Abstract]
Imputed interest rate applicable to facility lease obligation	11.00%
Facility lease obligation, including reimbursements	110,200,000	111,200,000
Facilities - Building C
Schedule of Facility Leases [Line Items]
2015	4,562,000
2016	4,688,000
2017	4,818,000
2018	4,951,000
2019	5,088,000
Thereafter	59,987,000
Total	84,094,000
Facility lease obligations [Abstract]
Imputed interest rate applicable to facility lease obligation	9.00%
Facility lease obligation, including reimbursements	49,300,000	49,100,000
Facilities Building D and E
Facility lease obligations [Abstract]
Facility lease obligation, including reimbursements	$152,800,000	$25,000,000

Commitments_and_Contingencies_3

Commitments and Contingencies - Research Collaboration and Licensing Agreements (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Agreements with Royalty Provisions
Research Collaboration and Licensing Arrangements [Line Items]
Royalty rate minimum	0.50%
Royalty rate maximum	16.50%
Royalty expense	$169,900,000	$128,100,000	$59,500,000
License agreement with Genentech - EYLEA
Research Collaboration and Licensing Arrangements [Line Items]
First payment made or maybe made upon reaching minimum sales target			60,000,000
Cumulative relevant sales minimum sales target			400,000,000
Cumulative sales range, 1st tier minimum	400,000,000
Sales range maximum 1st tier	3,000,000,000
Cumulative sales range, 2nd tier minimum	$3,000,000,000
Royalty payment percentage of cumulative sales within cumulative sales range	4.75%
Royalty payment percentage of cumulative sales over range	5.50%

Stockholders_Equity_Details

Stockholders' Equity (Details) (USD $)	1 Months Ended		12 Months Ended			1 Months Ended
	Nov. 30, 2014	Oct. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2007	Jan. 31, 2014
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			30,000,000	30,000,000
Number of demand rights to require the Company to conduct registered underwritten public offering			3
Debt Conversion			$230,600,000
Total convertible senior notes - par				400,000,000
Equity component of convertible senior notes, net of issuance costs		120,600,000
Proceeds received from the Warrant		93,800,000
Repayments of Convertible Debt			220,639,000	0	0
Gains (Losses) on Extinguishment of Debt			-33,469,000	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Payments for Repurchase of Warrants			294,552,000	0	0
Maximum reduction of warrants held by warrant holder	493,229
Maximum amount of warrant payable			-148,496,000
Maximum number of shares issuable upon exercise of warrants			3,540,095	4,760,840
Call option
Class of Stock [Line Items]
Purchase of convertible note hedges		117,500,000
Warrant Transactions
Class of Stock [Line Items]
Strike price of the warrant transaction (in dollars per share)		103.41
Proceeds received from the Warrant		93,800,000
Convertible senior notes
Class of Stock [Line Items]
Total convertible senior notes - par		400,000,000	169,400,000	400,000,000
Sanofi
Class of Stock [Line Items]
Number of shares of Common Stock purchased						12,000,000
Cash price of newly issued, unregistered shares of Common Stock purchased						312,000,000
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions			30.00%
Percentage Of Outstanding Shares Or Voting Rights Under Amended Investor Agreement			20.00%
Percentage Of Outstanding Shares that the Company is required to appoint an individual agreed upon by the Company and the Collaborator to the Company's board of directors			20.00%
Class A Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares)			40,000,000	40,000,000
Common Stock, par value (in dollars per share)			$0.00	$0.00
Common Stock, voting rights			ten votes per share
Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares)			160,000,000	160,000,000
Common Stock, par value (in dollars per share)			$0.00	$0.00
Common Stock, voting rights			one vote per share
Debt Conversion, Converted Instrument, Shares Issued			2,018,000
Bayer Collaboration Agreement - PDGFR-beta outside the US
Class of Stock [Line Items]
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions			20.00%				20.00%
Additional Paid-in Capital
Class of Stock [Line Items]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Maximum amount of warrant payable			($148,496,000)

LongTerm_Incentive_Plans_Detai

Long-Term Incentive Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of awards	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of shares outstanding at beginning of period	21,408,268
Number of shares granted	3,913,368	3,937,989	4,162,653
Number of shares forfeited	-252,126
Number of shares expired	-350
Number of shares exercised	-3,562,900
Number of shares outstanding at end of period	21,506,260	21,408,268
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average exercise price - outstanding at beginning of period	$98.10
Weighted average exercise price - granted	$385.33	$263.77	$167.96
Weighted average exercise price - forfeited	$155.37
Weighted average exercise price - expired	$64.35
Weighted average exercise price - exercised	$44.72
Weighted average exercise price - outstanding at end of period	$158.54	$98.10
Weighted average remaining contractual term (in years) - outstanding	6 years 11 months 26 days
Instrinsic value - outstanding	$5,467,783,000
Number of shares vested and expected to vest	20,988,044
Weighted average execise price - vested and expected to vest	$154.81
Weighted average remaining contractual term - vested and expected to vest	6 years 11 months 8 days
Intrinsic value - vested and expected to vest	5,414,258,000
Number of shares exercisable	12,104,560
Weighted average exercise price - exercisable	$65.48
Weighted average remaining contractual term - exercisable	5 years 6 months 10 days
Intrinsic value - exercisable	4,203,941,000
Total intrinsic value - of stock options exercised	1,081,200,000	727,500,000	566,700,000
Exercise Price Equal to Market Price [Abstract]
Number of Options Granted (shares)	3,913,368	3,937,989	4,162,653
Weighted Average Exercise Price (dollars per share)	$385.33	$263.77	$167.96
Weighted Average Fair Value	$140.38	$104.90	$67.66
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility	39.00%	42.00%	45.00%
Expected lives from grant date	5 years 2 months 11 days	5 years 4 months 1 day	5 years 4 months 24 days
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate	1.62%	1.73%	0.86%
Stock options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Stock options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Phantom stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period within vesting date that awards may be received	P30D
Non-performance based stock options
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Non-cash stock-based compensation expense	291,600,000	176,400,000	67,700,000
Unrecognized stock-based compensation cost, net of estimated forfeitures	706,000,000
Weighted average period for recognition of total unrecognized compensation expense (in years)	1 year 10 months 30 days
Performance-based stock options
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Non-cash stock-based compensation expense	4,100,000	8,000,000	15,300,000
Number of unvested options (shares)	0	770,250
Restricted stock
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Non-cash stock-based compensation expense	11,500,000	14,000,000	11,100,000
Unrecognized stock-based compensation cost, net of estimated forfeitures	$34,500,000
Weighted average period for recognition of total unrecognized compensation expense (in years)	2 years 9 months 2 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of shares outstanding at beginning of period	538,580
Number of shares granted	7,500
Number of shares vested	-20
Number of shares outstanding at end of period	546,060	538,580
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Weighted average grant date fair value at beginning of period	$112.16
Weighted average grant date fair value - granted	$338.32
Weighted average grant date fair value - vested	$237.68
Weighted average grant date fair value at end of period	$115.26	$112.16
Long-Term Incentive Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance	16,485,333			35,397,043
Number of shares available for future grants	13,558,022
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of shares exercised	-3,468,000	-3,052,000	-5,086,000
Common Stock | Long-Term Incentive Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance	4,485,333

Executive_Stock_Purchase_Plan_

Executive Stock Purchase Plan (Details) (Executive Stock Purchase Plan)	24 Months Ended
	Dec. 31, 1990	Dec. 31, 2014	Dec. 31, 1989
Executive Stock Purchase Plan
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Number of shares of Class A Stock reserved for restricted stock awards (in shares)			1,027,500
Number of shares issued (in shares)	983,254
Number of shares available for future grants under the Plan (in shares)		44,246

Employee_Savings_Plan_Details

Employee Savings Plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contribution expense to 401(k) Savings Plan	$13.10	$5.70	$6.30

Income_Taxes_Details

Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	$775,747,000	$713,360,000	$414,421,000
Current:
Federal	447,370,000	201,475,000	0
State	28,718,000	23,489,000	4,308,000
Current Foreign Tax Expense (Benefit)	2,879,000	433,000	0
Total current tax expense (benefit)	478,967,000	225,397,000	4,308,000
Deferred:
Federal	-68,700,000	54,910,000	-300,319,000
State	18,891,000	8,700,000	-39,837,000
Deferred Foreign Income Tax Expense (Benefit)	-1,485,000	-9,000	0
Total deferred tax expense (benefit)	-51,294,000	63,601,000	-340,156,000
Total income tax expense (benefit)	427,673,000	288,998,000	-335,848,000
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
U.S. federal statutory tax rate	35.00%	35.00%	35.00%
State and local income taxes	2.00%	3.40%	5.40%
Change in state effective rate	2.80%	0.00%	5.40%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	15.30%	4.90%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	-7.40%	-4.90%	0.00%
Reclassification of net operating losses related to exercises of stock options	0.00%	0.00%	9.30%
Provision (benefit) attributable to valuation allowances	0.00%	0.00%	-139.00%
Effective Income Tax Rate Reconciliation, Tax Contingency, Domestic, Percent	2.50%	0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent	2.70%	1.10%	0.00%
Other permanent differences	2.20%	1.00%	2.80%
Effective income tax rate	55.10%	40.50%	-81.10%
Deferred tax assets:
Net operating loss carry-forward	150,000	135,000
Fixed assets	8,078,000	18,902,000
Deferred revenue	75,503,000	88,033,000
Deferred compensation	194,489,000	109,715,000
Income tax credit carry-forwards	16,099,000	9,372,000
Capitalized research and development costs	12,908,000	18,942,000
Other	41,252,000	34,215,000
Deferred tax assets, gross	348,479,000	279,314,000
Valuation allowance	-359,000	-1,830,000
Deferred tax assets, net	348,120,000	277,484,000
Deferred tax liabilities:
Accruals	-28,186,000	0
Convertible senior notes	-252,000	-929,000
Deferred Tax Liabilities, Other	3,578,000	0
Deferred tax liabilities, gross	-32,016,000	-929,000
Deferred Tax Assets, Net	316,104,000	276,555,000
Utilization of net operating loss carryforwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of ISOs, credited to additional paid-in capital	448,556,000	216,857,000	4,308,000
Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount		34,000,000
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance			340,200,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	51,200,000	23,500,000	8,400,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		0
Other Comprehensive Income (Loss), Tax	27,100,000	0	0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	26,627,000	11,274,000	5,596,000
Gross increases related to current year tax positions	27,538,000	7,620,000	1,873,000
Gross increases related to prior year tax positions	6,464,000	8,305,000	3,805,000
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	3,014,000	572,000	0
Balance as of December 31	57,615,000	26,627,000	11,274,000
UNITED STATES
Operating Loss Carryforwards [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	1,115,958,000	812,278,000
Foreign
Operating Loss Carryforwards [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	($340,211,000)	($98,918,000)

Net_Income_Loss_Per_Share_Deta

Net Income (Loss) Per Share (Details) (USD $)	3 Months Ended												12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$110,176	[1]	$79,720	[1]	$92,735	[1]	$65,443	[1]	$96,806	$141,306	$87,376	$98,874	$348,074	$424,362	$750,269
Effect of dilutive securities:
Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs													0	0	29,126
Net income (loss) - diluted													$348,074	$424,362	$779,395
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares outstanding - basic													100,612	97,917	94,685
Effect of dilutive securities (in shares):
Stock options													9,440	10,233	14,231
Restricted stock													425	433	715
Convertible senior notes													0	0	4,761
Warrants													2,936	2,707	990
Dilutive potential shares													12,801	13,373	20,697
Weighted average shares - diluted (in shares)													113,413	111,290	115,382
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$1.09		$0.79		$0.92		$0.66		$0.98	$1.44	$0.89	$1.02	$3.46	$4.33	$7.92
Net income per share - diluted (in dollars per share)	$0.96		$0.70		$0.82		$0.58		$0.86	$1.25	$0.79	$0.90	$3.07	$3.81	$6.75
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													1,470	304	325
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares													4,247	4,761	0
[1]	Net income in the third quarter of 2014 included a $40.6 million incremental charge related to the Branded Prescription Drug Fee based on final regulations issued by the IRS in July 2014 as described in Note 3 above.

Statement_of_Cash_Flows_Detail

Statement of Cash Flows (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accrued capital expenditures	$56.20	$16.10	$8.60
Notes Payable	7.5
Capitalized and deferred interest	6.2	1.9	0
Facilities Building D and E
Facility lease obligations recognized	127.8	25	0
Warrant Transactions
Accounts Payable, Other	59.8
Liabilities, Fair Value Adjustment	$87.50

Unaudited_Quarterly_Results_De

Unaudited Quarterly Results (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Line Items]
Revenues	$802,329,000	[1]	$725,788,000	[1]	$665,700,000	[1]	$625,740,000	[1]	$610,412,000	[2]	$597,027,000	[2]	$457,642,000	[2]	$439,664,000	[2]	$2,819,557,000	$2,104,745,000	$1,378,477,000
Net income	110,176,000	[3]	79,720,000	[3]	92,735,000	[3]	65,443,000	[3]	96,806,000		141,306,000		87,376,000		98,874,000		348,074,000	424,362,000	750,269,000
Net income per share - basic	$1.09		$0.79		$0.92		$0.66		$0.98		$1.44		$0.89		$1.02		$3.46	$4.33	$7.92
Net income per share - diluted	$0.96		$0.70		$0.82		$0.58		$0.86		$1.25		$0.79		$0.90		$3.07	$3.81	$6.75
Substantive milestone payment	30,000,000		30,000,000		15,000,000		30,000,000		25,000,000		45,000,000
Branded Prescription Drug Fee																	40,600,000
Antibody Collaboration
Quarterly Financial Information Disclosure [Line Items]
Number of families of novel antibodies													2					2
Up-front payments made to acquire full rights to antibodies																	0	20,000,000	0
Ang2
Quarterly Financial Information Disclosure [Line Items]
Up-front payments made to acquire full rights to antibodies													10,000,000
PDGFR-beta
Quarterly Financial Information Disclosure [Line Items]
Up-front payments made to acquire full rights to antibodies													$10,000,000
[1]	Revenues in the first, second, third, and fourth quarters of 2014 included recognition of sales milestones of $30.0 million, $15.0 million, $30.0 million, and $30.0 million, respectively.
[2]	Revenues in the second quarter of 2013 were reduced by two $10 million up-front payments made to Sanofi to acquire full rights to antibodies to PDGF and antibodies to Ang2 in ophthalmology, as described in Note 4 above. Revenues in the third and fourth quarter of 2013 included recognition of sales and substantive development milestones of $45.0 million and $25.0 million, respectively.
[3]	Net income in the third quarter of 2014 included a $40.6 million incremental charge related to the Branded Prescription Drug Fee based on final regulations issued by the IRS in July 2014 as described in Note 3 above.