Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 15,081	$ 9,388
Marketable securities	146,302	83,181
Income tax receivable	664	731
Other receivables	926	123
Prepaid expenses	4,805	1,635
Restricted cash, current	361
Total current assets	168,139	95,058
Marketable securities, non-current	21,396
Property and equipment, net	880	1,177
Restricted cash	408	769
Total assets	190,823	97,004
Current liabilities:
Accounts payable and accrued expenses	13,622	8,506
Current portion of deferred revenue	26,825
Total current liabilities	40,447	8,506
Deferred revenue, non-current	15,184
Deferred lease obligation	1,562	1,718
Commitments and contingencies (Note 17)
Stockholders’ equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at December 31, 2018 and December 31, 2017; zero shares issued and outstanding at December 31, 2018 and December 31, 2017
Common stock; $0.001 par value; 100,000,000 shares authorized at December 31, 2018 and December 31, 2017; 39,547,558 shares and 32,662,255 shares issued and outstanding at December 31, 2018 and December 31, 2017, respectively	39	33
Additional paid-in capital	428,059	307,158
Accumulated deficit	(294,354)	(220,341)
Accumulated other comprehensive loss	(114)	(70)
Total stockholders’ equity	133,630	86,780
Total liabilities and stockholders’ equity	$ 190,823	$ 97,004