Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 33,255	$ 46,024
Marketable securities	43,351	51,666
Prepaid expenses and other current assets	1,367	1,656
Total current assets	77,973	99,346
Property and equipment, net	855	1,024
Other assets	564	305
Total assets	79,392	100,675
Current liabilities:
Accounts payable	3,738	3,139
Accrued contract research costs	12,511	12,317
Other accrued liabilities	5,408	6,177
Current portion of capital lease obligations	42	42
Current portion of term loans	9,221	9,214
Total current liabilities	30,920	30,889
Long-term liabilities:
Capital lease obligations, net of current portion	33	43
Term loans, net of current portion	2,299	4,607
Total long-term liabilities	2,332	4,650
Total liabilities	33,252	35,539
Stockholders' equity:
Preferred stock, par value $0.0001 per share Authorized: 5,000,000 shares at March 31, 2015 and December 31, 2014; no shares issued and outstanding at each of March 31, 2015 and December 31, 2014
Common stock, par value $0.0001 per share Authorized: 200,000,000 shares at March 31, 2015 and December 31, 2014; 109,120,670 shares issued and outstanding at each of March 31, 2015 and December 31, 2014	11	11
Additional paid-in-capital	704,403	702,694
Accumulated other comprehensive income	6	4
Accumulated deficit	(658,280)	(637,573)
Total stockholders' equity	46,140	65,136
Total liabilities and stockholders' equity	$ 79,392	$ 100,675