Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 96,811	$ 48,490
Marketable securities	15,249	42,986
Prepaid expenses and other current assets	2,264	765
Total current assets	114,324	92,241
Property and equipment, net	1,264	1,553
Other assets	358	1,409
Total assets	115,946	95,203
Current liabilities:
Accounts payable	5,226	6,589
Accrued contract research costs	12,987	10,407
Other accrued liabilities	5,212	5,718
Current portion of capital lease obligations	41	42
Current portion of term loans	9,200	9,451
Total current liabilities	32,666	32,207
Long-term liabilities:
Capital lease obligations, net of current portion	65	85
Term loans, net of current portion	9,217	13,820
Total long-term liabilities	9,282	13,905
Total liabilities	41,948	46,112
Stockholders' equity:
Preferred stock, par value $0.0001 per share Authorized: 5,000,000 shares at June 30, 2014 and December 31, 2013; no shares issued and outstanding at June 30, 2014 and December 31, 2013
Common stock, par value $0.0001 per share Authorized: 200,000,000 shares at June 30, 2014 and December 31, 2013; 101,309,750 and 85,232,506 shares issued and outstanding at June 30, 2014 and December 31, 2013, respectively	10	9
Additional paid-in-capital	671,240	600,477
Accumulated other comprehensive income	3	17
Accumulated deficit	(597,255)	(551,412)
Total stockholders' equity	73,998	49,091
Total liabilities and stockholders' equity	$ 115,946	$ 95,203