Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 17,036	$ 18,305
Marketable securities	103,160	136,701
Income tax receivable	938	816
Other receivables	847	971
Prepaid expenses	10,688	8,863
Total current assets	132,669	165,656
Operating lease right-of-use asset	2,876	3,036
Marketable securities, non-current	59,568	63,159
Property and equipment, net	652	700
Restricted cash	408	408
Total assets	196,173	232,959
Current liabilities:
Accounts payable and accrued expenses	17,371	19,665
Operating lease liability, current	991	967
Current portion of deferred revenue	14,241	22,262
Total current liabilities	32,603	42,894
Operating lease liability, non-current	3,096	3,352
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at March 31, 2020 and December 31, 2019, zero shares issued and outstanding at March 31, 2020 and December 31, 2019
Common stock; $0.001 par value; 100,000,000 shares authorized at March 31, 2020 and December 31, 2019, 46,727,725 shares and 46,720,225 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	47	47
Additional paid-in capital	590,144	587,223
Accumulated deficit	(429,649)	(400,727)
Accumulated other comprehensive income (loss)	(68)	170
Total stockholders' equity	160,474	186,713
Total liabilities and stockholders' equity	$ 196,173	$ 232,959