Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 23,844	$ 23,179
Restricted cash	151	54
Short-term investments	81,486	63,310
Prepaid expenses and other current assets	3,029	1,464
Total current assets	108,510	88,007
Property and equipment, net	260	88
Other assets	243	1,808
Total assets	109,013	89,903
Current liabilities:
Accounts payable	2,375	1,452
Accrued expenses and other current liabilities	6,771	2,175
Current portion of deferred revenue	1,220	1,220
Total current liabilities	10,366	4,847
Long-term liabilities:
Common stock warrant liability		2,848
Deferred revenue, less current portion	14,220	15,440
Other long-term liabilities	288	70
Total long-term liabilities	14,508	18,358
Total liabilities	24,874	23,205
Commitments (Note 16)
Convertible preferred stock (Note 12)		319,113
Stockholders' equity (deficit):
Preferred stock, value	0	0
Common stock, $0.0001 par value, 100,000,000 and 20,800,000 shares authorized; 18,215,181 and 85,440 shares outstanding at December 31, 2016 and December 31, 2015, respectively	2	1
Additional paid-in capital	389,374
Accumulated other comprehensive income	56	28
Accumulated deficit	(305,293)	(259,675)
Total stockholders' equity (deficit)	84,139	(252,415)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 109,013	89,903
Series A Convertible Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock, value		7,231
Total stockholders' equity (deficit)		$ 7,231