Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 18,494	$ 15,081
Marketable securities	96,815	146,302
Income tax receivable	984	664
Other receivables	605	926
Prepaid expenses	7,512	4,805
Restricted cash, current	361	361
Total current assets	124,771	168,139
Operating lease right-of-use asset	3,344
Marketable securities, non-current	20,320	21,396
Property and equipment, net	798	880
Restricted cash	408	408
Total assets	149,641	190,823
Current liabilities:
Accounts payable and accrued expenses	12,766	13,622
Operating lease liability, current	923
Current portion of deferred revenue	26,473	26,825
Total current liabilities	40,162	40,447
Operating lease liability, non-current	3,849
Deferred revenue, non-current	6,085	15,184
Deferred lease obligation		1,562
Commitments and contingencies (Note 15)
Stockholders’ equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at June 30, 2019 and December 31, 2018, zero shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock; $0.001 par value; 100,000,000 shares authorized at June 30, 2019 and December 31, 2018, 40,027,916 shares and 39,547,558 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	40	39
Additional paid-in capital	438,614	428,059
Accumulated deficit	(339,274)	(294,354)
Accumulated other comprehensive income (loss)	165	(114)
Total stockholders’ equity	99,545	133,630
Total liabilities and stockholders’ equity	$ 149,641	$ 190,823