Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 25,477	$ 81,512
Marketable securities	27,907	19,087
Prepaid expenses and other current assets	1,358	786
Total current assets	54,742	101,385
Property and equipment, net	1,488	1,174
Other assets	433	458
Total assets	56,663	103,017
Current liabilities:
Accounts payable	5,693	5,661
Accrued contract research costs	8,352	4,761
Other accrued liabilities	4,497	5,127
Current portion of capital lease obligations	4	13
Current portion of term loans	7,385	7,924
Total current liabilities	25,931	23,486
Long-term liabilities:
Capital lease obligations, net of current portion		1
Term loans, net of current portion	16,120	4,464
Total long-term liabilities	16,120	4,465
Total liabilities	42,051	27,951
Stockholders' equity:
Preferred stock, par value $0.0001 per share Authorized: 5,000,000 shares at September 30, 2013 and December 31, 2012; no shares issued and outstanding at September 30, 2013 and December 31, 2012
Common stock, par value $0.0001 per share Authorized: 200,000,000 shares at September 30, 2013 and 100,000,000 shares at December 31, 2012; 69,103,073 and 68,930,082 shares issued and outstanding at September 30, 2013 and December 31, 2012, respectively	7	7
Additional paid-in-capital	541,849	536,277
Accumulated other comprehensive income	6	2
Accumulated deficit	(527,250)	(461,220)
Total stockholders' equity	14,612	75,066
Total liabilities and stockholders' equity	$ 56,663	$ 103,017