Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net loss	$ (38,841)	$ (34,037)	$ (54,753)
Adjustments to reconcile net loss to net cash flows used in operating activities:
Amortization of deferred revenue	(60,389)	(62,508)	(69,254)
Stock-based compensation	13,885	13,530	10,726
Depreciation and amortization	430	465	311
Accretion of discount on securities	(65)	(281)	(1,081)
Changes in operating assets and liabilities:
Receivable from collaboration partners	8,643	(14,698)	(2,968)
Prepaid expenses and other current assets	(1,945)	(224)	(5,450)
Other assets	166	(322)	78
Accounts payable	2,359	(1,611)	(2,326)
Accrued expenses	2,504	9,345	6,282
Other current liabilities	(4,923)	4,393	706
Deferred revenue	3,000	10,000	110,000
Other non-current liabilities	(785)	884	144
Net cash used in operating activities	(75,961)	(75,064)	(7,585)
Cash flows from investing activities:
Purchase of short-term investments	(74,956)	(209,888)	(342,437)
Maturities of short-term investments	100,075	331,000	272,000
Purchase of property and equipment	(286)	(197)	(631)
Change in restricted cash	(5,146)	1,500	(1,500)
Net cash provided by (used in) investing activities	19,687	122,415	(72,568)
Cash flows from financing activities:
Proceeds from stock option and warrant exercises	15,734	2,625	3,389
Net proceeds from stockholder securities law settlement	2,959
Proceeds from issuance of common stock, net of issuance costs			62,059
Excess tax benefits from stock-based compensation		278	714
Net cash provided by financing activities	18,693	2,903	66,162
Net (decrease) increase in cash and cash equivalents	(37,581)	50,254	(13,991)
Cash and cash equivalents at beginning of year	107,717	57,463	71,454
Cash and cash equivalents at end of year	70,136	107,717	57,463
Supplemental disclosures of cash flow information:
Income taxes paid	5,358		8,400
Receivable from stock option exercises			$ 436