September 2009 Financial Transactions (Details) (USD $)	1 Months Ended			3 Months Ended		12 Months Ended
	Oct. 31, 2011	Feb. 28, 2011	Sep. 30, 2009 agreements	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
2012 Notes
Face amount of 2012 Notes			$ 155,000,000
Proceeds from issuance of 2012 Notes			122,200,000
Proceeds from milestone payment		50,000,000
Portion of 2012 Notes redeemed upon achievement of certain approval milestone pursuant to the Janssen collaboration					50,000,000
Milestone payment redeemed in the fourth quarter of 2011	105,000,000
Sale of Contingent Milestone Payments
Number of purchase agreements entered into related to sale of contingent launch milestone payments pursuant to the Janssen collaboration			2
Proceeds from sale of potential contingent launch milestone payments pursuant to the Janssen collaboration			32,800,000
Value of potential contingent launch milestone payments sold pursuant to the Janssen collaboration			95,000,000
Third party's proceeds from the milestone payments from Janssen in the fourth quarter of 2011						95,000,000
Expenses and Losses (Gains):
Interest expense related to 2012 Notes				0	7,934,000
Change in fair value of embedded derivative related to 2012 Notes				0	(1,496,000)
Change in fair value of free-standing derivatives related to the sale of milestone payments				0	7,094,000
Total September 2009 financial transaction expenses				$ 0	$ 13,532,000