Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 34,705	$ 15,081
Marketable securities	158,384	146,302
Income tax receivable	1,033	664
Other receivables	784	926
Prepaid expenses	8,556	4,805
Restricted cash, current		361
Total current assets	203,462	168,139
Operating lease right-of-use asset	3,192
Marketable securities, non-current	55,985	21,396
Property and equipment, net	748	880
Restricted cash	408	408
Total assets	263,795	190,823
Current liabilities:
Accounts payable and accrued expenses	20,581	13,622
Operating lease liability, current	945
Current portion of deferred revenue	26,773	26,825
Total current liabilities	48,299	40,447
Operating lease liability, non-current	3,602
Deferred revenue, non-current	0	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 September 30, 2019 and December 31, 2018, zero shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock; $0.001 par value; 100,000,000 shares authorized at September 30, 2019 and December 31, 2018, 46,673,977 shares and 39,547,558 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	46	39
Additional paid-in capital	583,811	428,059
Accumulated deficit	(372,116)	(294,354)
Accumulated other comprehensive income (loss)	153	(114)
Total stockholders’ equity	211,894	133,630
Total liabilities and stockholders’ equity	$ 263,795	$ 190,823