Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 24,266	$ 46,774
Marketable securities	86,335	125,864
Prepaid expenses and other current assets	1,788	1,893
Total current assets	112,389	174,531
Property and equipment, net	1,059	696
Restricted cash	1,193	112
Intangible asset, net	13	15
Total assets	114,654	175,354
Current liabilities:
Accounts payable	8,749	6,750
Accrued expenses and other current liabilities	8,208	3,030
Current portion of loans payable, net	5,039
Deferred revenue		3,750
Deferred rent	52	44
Total current liabilities	22,048	13,574
Loan payable, net	13,270	18,186
Capital leases, net of current portion	18	8
Deferred rent, net of current portion	187	239
Warrant liability	75	153
Other long term liabilities	475	63
Total liabilities	36,073	32,223
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock—$0.001 par value; 100,000,000 shares authorized, 55,768,414 and 50,802,603 shares issued and outstanding at December 31, 2016 and December 31, 2015, respectively	56	51
Preferred stock—$0.001 par value; 5,000,000 shares authorized, none issued or outstanding at December 31, 2016 and December 31, 2015
Additional paid-in capital	364,148	325,784
Accumulated deficit	(285,625)	(182,498)
Accumulated other comprehensive income (loss)	2	(206)
Total stockholders' equity	78,581	143,131
Total liabilities, redeemable convertible preferred stock and stockholders' equity	$ 114,654	$ 175,354