Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 12,156	$ 24,023
Marketable securities	31,771	39,934
Prepaid expenses and other current assets	2,259	3,213
Total current assets	46,186	67,170
Property and equipment, net	401	489
Restricted cash	270	270
Other assets		45
Total assets	46,857	67,974
Current liabilities:
Accounts payable	1,846	1,208
Accrued expenses	5,971	4,954
Total current liabilities	7,817	6,162
Long-term liabilities	156	88
Total liabilities	7,973	6,250
Commitments and contingencies (Note 6)
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 200,000,000 shares authorized; 22,634,825 and 22,597,144 shares issued and outstanding at June 30, 2016 and December 31, 2015, respectively	23	23
Additional paid-in capital	195,245	193,194
Accumulated other comprehensive income (loss)	6	(55)
Accumulated deficit	(156,390)	(131,438)
Total stockholders' equity	38,884	61,724
Total liabilities and stockholders' equity	$ 46,857	$ 67,974