Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities:
Net loss	$ (35,750)	$ (24,854)	$ (18,587)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	646	676	572
Amortization of premium / discount on marketable securities	1,576	1,187	288
Stock-based compensation	8,081	7,818	8,467
Net loss on disposal of property and equipment			34
Other			(302)
Net changes in operating assets and liabilities:
Interest receivable	6	4	(147)
Accounts receivable	(553)	(297)	431
Prepaid expenses and other assets	(13)	97	(96)
Accounts payable and accrued liabilities	(139)	3,196	(1,390)
Accrued compensation and employee benefits	315	(28)	997
Deferred revenue	(64)	(11,733)	3,596
Net cash used in operating activities	(25,895)	(23,934)	(6,137)
Investing activities:
Purchases of marketable securities	(112,974)	(100,027)	(79,406)
Maturities of marketable securities	83,411	113,096	60,500
Proceeds from sales of marketable securities	10,139
Purchases of property and equipment	(576)	(695)	(272)
Net cash provided by / (used in) investing activities	(20,000)	12,374	(19,178)
Financing activities:
Issuance of common stock	51,877	1,185	21,846
Net cash provided by financing activities	51,877	1,185	26,763
Effect of exchange rate changes on cash			302
Net increase / (decrease) in cash and cash equivalents	5,982	(10,375)	1,750
Cash and cash equivalents, beginning of period	10,784	21,159	19,409
Cash and cash equivalents, end of period	16,766	10,784	21,159
License Agreements [Member]
Financing activities:
Issuance of common stock			$ 4,917