Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities:
Net loss	$ (27,970)	$ (30,148)
Adjustments to reconcile net loss to net cash flows used in operating activities:
Amortization of deferred revenue	(45,448)	(45,876)
Stock-based compensation	10,516	9,972
Depreciation and amortization	324	355
Accretion of discount on securities	(50)	(230)
Changes in operating assets and liabilities:
Receivable from collaboration partners	7,051	(11,375)
Prepaid expenses and other current assets	3,103	(4,849)
Other non-current assets	(3,411)	(352)
Accounts payable	2,082	642
Accrued expenses	5,747	10,558
Other current liabilities	(4,354)	(642)
Deferred revenue	3,000
Other non-current liabilities	(810)	424
Net cash used in operating activities	(50,220)	(71,521)
Cash flows from investing activities:
Purchase of short-term investments	(74,881)	(69,962)
Maturities of short-term investments	100,000	241,000
Purchase of property and equipment	(137)	(150)
Net cash provided by investing activities	24,982	170,888
Cash flows from financing activities:
Stock option exercises	2,933	3,061
Net proceeds from stockholder securities law settlement	2,959
Excess tax benefits from stock-based compensation		45
Net cash provided by financing activities	5,892	3,106
Net (decrease) increase in cash and cash equivalents	(19,346)	102,473
Cash and cash equivalents at beginning of period	107,717	57,463
Cash and cash equivalents at end of period	$ 88,371	$ 159,936