Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 75,281	$ 18,305
Marketable securities	45,588	136,701
Income tax receivable	1,252	816
Other receivables	462	971
Prepaid expenses	10,254	8,863
Total current assets	132,837	165,656
Operating lease right-of-use asset	2,654	3,036
Marketable securities, non-current	10,506	63,159
Property and equipment, net	731	700
Restricted cash	408	408
Total assets	147,136	232,959
Current liabilities:
Accounts payable and accrued expenses	15,057	19,665
Operating lease liability, current	1,030	967
Current portion of deferred revenue	511	22,262
Total current liabilities	16,598	42,894
Operating lease liability, non-current	2,691	3,352
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at September 30, 2020 and December 31, 2019, zero shares issued and outstanding at September 30, 2020 and December 31, 2019
Common stock; $0.001 par value; 100,000,000 shares authorized at September 30, 2020 and December 31, 2019, 46,892,552 shares and 46,720,225 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively	47	47
Additional paid-in capital	598,663	587,223
Accumulated deficit	(471,226)	(400,727)
Accumulated other comprehensive income	363	170
Total stockholders' equity	127,847	186,713
Total liabilities and stockholders' equity	$ 147,136	$ 232,959