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	$ (23,509)	$ (2,232)	$ (5,100)
Adjustments to reconcile net loss tonet cash (used in) provided by operating activities:
Depreciation and amortization	193	484	732
Amortization of intangible assets	111	111	111
Noncash interest expense	22	0
Amortization of premium on marketable securities	237	429	375
Stock based compensation expense	821	221	299
Gains on disposal of fixed assets	(146)		(4)
Change in fair value of preferred stock warrant liabilities	(39)	48	(2)
Changes in operating assets and liabilities:
Contract receivables	90	332	(509)
Prepaid expenses and other current assets	(291)	(11)	(102)
Accounts payable	2,007	(908)	487
Accrued compensation	(205)	95	107
Deferred revenue	(5,630)	(13,977)	19,607
Accrued research and clinical liabilities	2,459	45	(1,072)
Other liabilities	27	11	(257)
Deferred rent	(53)	22	(271)
Net cash (used in) provided by operating activities	(23,906)	(15,330)	14,401
Investing activities:
Purchases of property and equipment	(20)	(463)	(68)
Proceeds from sale of property and equipment	170
Purchases of marketable securities	(25,507)	(26,974)	(59,344)
Proceeds from maturities of marketable securities	30,432	36,891	49,225
Changes in restricted cash		278	(183)
Net cash provided by (used in) investing activities	5,075	9,732	(10,370)
Financing activities:
Payments of deferred offering costs	(2,329)
Proceeds from issuance of debt	9,840
Proceeds from issuances of Series E preferred stock, net	18,845
Proceeds from issuances of common stock	84	34	119
Net cash provided by financing activities	26,440	34	119
Net increase (decrease) in cash and cash equivalents	7,609	(5,564)	4,150
Cash and cash equivalents, beginning of period	3,338	8,902	4,752
Cash and cash equivalents, end of period	10,947	3,338	8,902
Supplemental cash flow disclosure:
Cash paid for interest	109
Supplemental disclosure of noncash investing and financing activities:
Warrant issued upon issuance of note payable	$ 79