Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 31,683	$ 18,305
Marketable securities	149,242	136,701
Income tax receivable	1,507	816
Other receivables	557	971
Prepaid expenses	12,076	8,863
Total current assets	195,065	165,656
Operating lease right-of-use assets	4,279	3,036
Marketable securities, non-current	70,565	63,159
Property and equipment, net	840	700
Restricted cash	408	408
Total assets	271,157	232,959
Current liabilities:
Accounts payable and accrued expenses	16,881	19,665
Operating lease liabilities, current	1,602	967
Current portion of deferred revenue		22,262
Total current liabilities	18,483	42,894
Operating lease liabilities, non-current	3,673	3,352
Commitments and contingencies (Note 17)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at December 31, 2020 and December 31, 2019, zero shares issued and outstanding at December 31, 2020 and December 31, 2019
Common stock; $0.001 par value; 100,000,000 shares authorized at December 31, 2020 and December 31, 2019, 49,872,213 shares and 46,720,225 shares issued and outstanding at December 31, 2020 and December 31, 2019, respectively	50	47
Additional paid-in capital	641,195	587,223
Accumulated deficit	(392,317)	(400,727)
Accumulated other comprehensive income	73	170
Total stockholders' equity	249,001	186,713
Total liabilities and stockholders' equity	$ 271,157	$ 232,959