Collaboration and License Agreements (Details) (USD $)	3 Months Ended		1 Months Ended			3 Months Ended		12 Months Ended		3 Months Ended			1 Months Ended		3 Months Ended		1 Months Ended	3 Months Ended			1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Oct. 31, 2011 2003 Sandoz Collaboration Item	Jul. 31, 2011 2003 Sandoz Collaboration Item	Jul. 31, 2010 2003 Sandoz Collaboration Item	Mar. 31, 2013 2003 Sandoz Collaboration Item	Mar. 31, 2012 2003 Sandoz Collaboration	Dec. 31, 2011 2003 Sandoz Collaboration	Mar. 31, 2013 2003 Sandoz Collaboration Maximum	Mar. 31, 2013 Second Sandoz Collaboration Agreement Item	Mar. 31, 2012 Second Sandoz Collaboration Agreement	Mar. 31, 2013 Second Sandoz Collaboration Agreement Maximum	Mar. 31, 2013 Second Sandoz Collaboration Agreement Novartis Pharma AG	Jul. 31, 2006 Second Sandoz Collaboration Agreement Novartis Pharma AG	Mar. 31, 2013 Second Sandoz Collaboration Agreement Novartis Pharma AG	Mar. 31, 2012 Second Sandoz Collaboration Agreement Novartis Pharma AG	Mar. 31, 2013 Second Sandoz Collaboration Agreement Novartis Pharma AG Change in estimate	Mar. 31, 2013 Second Sandoz Collaboration Agreement Novartis Pharma AG Change in estimate	Mar. 31, 2013 Massachusetts Institute of Technology Item	Mar. 31, 2012 Massachusetts Institute of Technology	Jul. 31, 2012 Baxter Agreement Item	Mar. 31, 2013 Baxter Agreement Item	Mar. 31, 2013 Baxter Agreement Accounting Standards Update No. 2009-13 Item	Mar. 31, 2012 Baxter Agreement Accounting Standards Update No. 2009-13	Mar. 31, 2013 Baxter Agreement Maximum
Collaborations and License Agreements
Number of significant deliverables identified in arrangement						2				2
Number of third-party competitors			0	0	0
Percentage of contractual profits earned under collaborative arrangement						45.00%									50.00%
Profit-share product revenue earned from the collaborative agreement, net of development and legal expenses						$ 5,400,000	$ 22,000,000
Percentage of royalty for net sales up to pre-defined sales threshold						10.00%
Percentage of royalty for net sales above pre-defined sales threshold						12.00%
Milestone payments possible per agreement									55,000,000			163,000,000
Period since date of product approval during which no competitor marketed similar product				1 year
Manufacturing raw material purchases						0
Sales-based and commercial milestone payments possible per agreement												153,000,000
Number of shares sold														4,708,679
Per share price of shares sold														$ 15.93
Closing price of the company's common stock on the NASDAQ Global Market (in dollars per share)														$ 13.05
Aggregate purchase price of shares sold														75,000,000
Premium paid														13,600,000
Estimated development period for recognition of paid premium													6 years				7 years
Change in net income (loss)	24,116,000	4,982,000																200,000
Research and development revenue related to paid premium recognized															300,000	500,000
Regulatory milestone payments possible per agreement												10,000,000
Number of follow-on biologic products for development and commercialization																					1	2
Period of right to select additional follow-on biologic products																						3 years
Number of additional follow-on biologic products to be included in the collaboration																						3
Percentage share of Company's option to participate, at its discretion, in a cost and profit share arrangement for the four additional products																									30.00%
Total arrangement consideration																							61,000,000
Portion of arrangement consideration allocated to the first initial product license																							10,300,000
Portion of arrangement consideration allocated to each of the four additional product licenses																							10,300,000
Portion of arrangement consideration allocated to the second initial product license																							9,400,000
Portion of arrangement consideration allocated to the joint steering committee unit of accounting																							114,000
Upfront payment paid by Baxter to the company																						33,000,000
Option payments agreed to be paid by Baxter with respect to additional product candidates																						28,000,000
Option payments agreed to be paid for each of the extensions of the period																						5,000,000
Technical and development milestone payment agreed to be paid by Baxter																						80,000,000
Number of product candidates																						6
Aggregate regulatory milestones to be paid by Baxter																						300,000,000
Number of follow-on biologic products for development and product licenses																					1		2
Number of additional follow-on biologic products for development and product licenses																							3
Number of follow-on biologic products for research and development services																							2
Number of additional follow-on biologic products for research and development services																						4
Number of combined units of accounting for performance period																							6
Number of initial product estimate for performance period																						0	2
Number of vendors selling similar, competing products on a stand-alone basis																						0
Remaining payment obligation																						0
Estimate performance period for the first initial product																							5 years
Estimate performance period for the second initial product																							7 years
Estimate performance period for the joint steering committee																							9 years
Total potential license fees and milestones receivable upon the achievement of pre-defined minimum development																						26,000,000
Potential milestone payments, in aggregate																						380,000,000
First anticipated technical and development milestone payment																						7,000,000
Period of right of first negotiation with respect to collaborating in development of a competing product																						3 years
Number of license agreements																						6
Number of accounting units for revenue recognition																						6
Number of other time-based milestones																						0
License, maintenance and royalties recorded
License and maintenance fees																			21,000	39,000
Royalties																			108,000	441,000
Total																			129,000	480,000
Annual license maintenance fee																			100,000
Number of patents issued in the United States																			30
Term of patents from the filing date of application																			20 years
Period of nonpayment considered for immediately terminating the agreement																			60 days
Period of material breach considered for immediately terminating the agreement																			90 days
Revenue earned and recognized upon achievement of a commercial milestone								10,000,000
Revenue earned and recognized upon the achievement of a regulatory milestone					5,000,000
Revenue earned and recognized upon amortization of the upfront payment																							700,000	600,000
Shared development costs	$ 22,332,000	$ 18,562,000								$ 0	$ 0