Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 14,440	$ 21,464
Restricted cash	361	361
Short-term marketable securities	11,649	11,577
Prepaid expenses and other current assets	940	451
Total current assets	27,390	33,853
Long-term marketable securities	751
Property, equipment and leasehold improvements, net	395	510
Other assets	415	421
Total assets	28,951	34,784
Current liabilities:
Accounts payable	1,038	1,011
Loan payable, current portion	430	423
Derivative warrant liability	1,073	1,314
Deferred rent, current portion	147	141
Accrued expenses	1,421	1,959
Total current liabilities	4,109	4,848
Loan payable, net of current portion	742	852
Deferred rent, net of current portion	95	135
Other liabilities	36
Total liabilities	4,982	5,835
Commitments and contingencies
Stockholders' equity:
Common stock, $0.00001 par value, authorized 100,000,000 shares; issued and outstanding 32,123,392 shares at March 31, 2017; issued and outstanding 32,044,087 shares at December 31, 2016	1	1
Accumulated other comprehensive loss	(2)
Additional paid-in capital	187,523	185,955
Accumulated deficit	(163,553)	(157,007)
Total stockholders' equity	23,969	28,949
Total liabilities and stockholders' equity	$ 28,951	$ 34,784