Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 21,464	$ 14,920
Restricted cash	361	361
Marketable securities	11,577	5,274
Prepaid expenses and other current assets	451	184
Total current assets	33,853	20,739
Property, equipment and leasehold improvements, net	510	938
Other assets	421	115
Total assets	34,784	21,792
Current liabilities:
Accounts payable	1,011	521
Loan payable, current portion	423	395
Derivative warrant liability	1,314	1,907
Deferred rent, current portion	141	115
Accrued expenses	1,959	374
Total current liabilities	4,848	3,312
Loan payable, net of current portion	852	1,275
Deferred rent, net of current portion	135	276
Total liabilities	5,835	4,863
Commitments and contingencies
Stockholders' equity:
Common stock, $0.00001 par value, authorized 100,000,000 shares, issued and outstanding 32,044,087 shares at December 31, 2016; and authorized 50,000,000 shares, issued and outstanding 27,555,948 shares at December 31, 2015	1	1
Additional paid-in capital	185,955	150,497
Accumulated deficit	(157,007)	(133,569)
Total stockholders' equity	28,949	16,929
Total liabilities and stockholders' equity	$ 34,784	$ 21,792