Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Cash flows from operating activities:
Net income (loss)	$ 440	$ (8,452)
Adjustments for non-cash operating items:
Amortization of deferred revenue	(36,825)	(14,709)
Stock-based compensation	4,336	3,614
Amortization of debt discount and debt issuance costs	359
Depreciation on property and equipment	117	109
Accretion of discount on investment securities	(13)	(35)
Changes in operating assets and liabilities:
Receivables from collaboration partners	(1,970)	6,441
Prepaid expenses and other current assets	961	88
Other non-current assets	92	(899)
Accounts payable	3,409	1,650
Accrued expenses	8,243	305
Other current liabilities	827	(4,740)
Other non-current liabilities	(237)	(26)
Net cash used in operating activities	(20,261)	(16,654)
Cash flows from investing activities:
Purchases of short-term investments	(149,950)
Maturities of short-term investments	25,000
Purchases of property and equipment	(1,255)
Change in restricted cash	(816)
Net cash used in investing activities	(127,021)
Cash flows from financing activities:
Proceeds from issuance of Convertible Notes, net	250,987
Financing transaction costs	(488)
Proceeds from stock option exercises	6,794	863
Net proceeds from stockholder securities law settlement		2,959
Net cash provided by financing activities	257,293	3,822
Net increase (decrease) in cash and cash equivalents	110,011	(12,832)
Cash and cash equivalents at beginning of period	70,136	107,717
Cash and cash equivalents at end of period	$ 180,147	$ 94,885