Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 56,967	$ 18,305
Marketable securities	73,218	136,701
Income tax receivable	1,120	816
Other receivables	486	971
Prepaid expenses	10,124	8,863
Total current assets	141,915	165,656
Operating lease right-of-use asset	2,825	3,036
Marketable securities, non-current	22,861	63,159
Property and equipment, net	604	700
Restricted cash	408	408
Total assets	168,613	232,959
Current liabilities:
Accounts payable and accrued expenses	13,952	19,665
Operating lease liability, current	1,006	967
Current portion of deferred revenue	9,768	22,262
Total current liabilities	24,726	42,894
Operating lease liability, non-current	2,959	3,352
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at June 30, 2020 and December 31, 2019, zero shares issued and outstanding at June 30, 2020 and December 31, 2019
Common stock; $0.001 par value; 100,000,000 shares authorized at June 30, 2020 and December 31, 2019, 46,864,405 shares and 46,720,225 shares issued and outstanding at June 30, 2020 and December 31, 2019, respectively	47	47
Additional paid-in capital	594,963	587,223
Accumulated deficit	(454,717)	(400,727)
Accumulated other comprehensive income	635	170
Total stockholders' equity	140,928	186,713
Total liabilities and stockholders' equity	$ 168,613	$ 232,959