Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 33,397	$ 54,220
Marketable securities	29,303	22,511
Prepaid expenses and other current assets	765	786
Restricted cash	205	205
Total current assets	63,670	77,722
Restricted cash	193
Property and equipment, net	210	276
Marketable securities, non-current	1,692
Other assets	814	706
Total assets	66,579	78,704
Current liabilities:
Accounts payable	1,634	3,197
Accrued compensation	637	1,091
Accrued research and clinical liabilities	3,691	3,309
Notes payable, short-term	3,187	3,182
Other accrued liabilities	750	603
Total current liabilities	9,899	11,382
Notes payable, long-term	6,006	6,786
Total liabilities	15,905	18,168
Commitments and contingencies (Note 7)
Stockholders' equity (deficit):
Common stock, $0.001 par value: 47,500,000 shares authorized at March 31, 2014 and December 31, 2013; 32,981,396 and 32,931,092 shares issued and outstanding at March 31,2014, and December 31, 2013, respectively	33	33
Additional paid-in capital	201,265	200,715
Accumulated other comprehensive income (loss)	(1)	3
Accumulated deficit	(150,623)	(140,215)
Total stockholders' equity	50,674	60,536
Total liabilities and stockholders' equity	$ 66,579	$ 78,704