Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 10,947	$ 3,338
Marketable securities	9,351	14,509
Contract receivables	87	177
Prepaid expenses and other current assets	871	580
Total current assets	21,256	18,604
Restricted cash	205	205
Property and equipment, net	230	427
Deferred offering costs	2,803	0
Intangible and other assets	45	111
Total assets	24,539	19,347
Current liabilities:
Accounts payable	2,448	266
Accrued compensation	628	832
Deferred revenue, short-term		5,630
Deferred rent, short-term	101	53
Accrued research and clinical liabilities	3,538	1,079
Other accrued liabilities	502	248
Total current liabilities	7,217	8,108
Deferred rent, long-term	62	163
Notes payable	9,826
Other liabilities, long-term	355	243
Total liabilities	17,460	8,514
Commitments and contingencies (Note 9)
Convertible preferred stock, $0.001 par value: 60,152,555 shares and 39,108,536 sharesauthorized at December 31, 2012, and 2011, respectively; 12,329,330 shares and 10,657,030 shares issued and outstanding at December 31, 2012, and 2011, respectively; aggregate liquidation preference of $105,512 at December 31, 2012	102,023	83,178
Stockholders' deficit:
Common stock, $0.001 par value: 80,000,000 shares 60,000,000 shares authorized at December 31, 2012, and 2011, respectively; 2,186,695 and 1,986,431 shares issued and outstanding at December 31, 2012, and 2011, respectively	2	2
Additional paid-in capital	3,317	2,412
Accumulated other comprehensive income (loss)	4	(1)
Accumulated deficit	(98,267)	(74,758)
Total stockholders' deficit	(94,944)	(72,345)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 24,539	$ 19,347