Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities:
Net loss	$ (22,264)	$ (35,750)	$ (24,854)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	660	646	676
Amortization of premium/discount on marketable securities	889	1,576	1,187
Stock-based compensation	5,338	8,081	7,818
Net loss on disposal of property and equipment	123
Net changes in operating assets and liabilities:
Interest receivable	141	6	4
Accounts receivable	(3,414)	(553)	(297)
Prepaid expenses and other assets	14	(13)	97
Accounts payable and accrued liabilities	(1,503)	(139)	3,196
Accrued compensation and employee benefits	800	315	(28)
Deferred revenue	11,134	(64)	(11,733)
Net cash used in operating activities	(8,082)	(25,895)	(23,934)
Investing activities:
Purchases of marketable securities	(91,428)	(112,974)	(100,027)
Maturities of marketable securities	103,470	83,412	113,096
Proceeds from sales of marketable securities		10,139
Purchases of property and equipment	(723)	(576)	(695)
Net cash provided by / (used in) investing activities	11,319	(19,999)	12,374
Financing activities:
Proceeds from issuance of common stock	1,676	51,876	1,185
Net cash provided by financing activities	1,676	51,876	1,185
Net increase / (decrease) in cash and cash equivalents	4,913	5,982	(10,375)
Cash and cash equivalents, beginning of period	16,766	10,784	21,159
Cash and cash equivalents, end of period	$ 21,679	$ 16,766	$ 10,784