Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 22,519	$ 31,683
Marketable securities	149,063	149,242
Income tax receivable	1,507	1,507
Other receivables	2,244	557
Prepaid expenses	13,018	12,076
Total current assets	188,351	195,065
Operating lease right-of-use assets	3,963	4,279
Marketable securities, non-current	56,728	70,565
Property and equipment, net	778	840
Restricted cash	408	408
Total assets	250,228	271,157
Current liabilities:
Accounts payable and accrued expenses	14,880	16,881
Operating lease liabilities, current	1,639	1,602
Total current liabilities	16,519	18,483
Operating lease liabilities, non-current	3,250	3,673
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at March 31, 2021 and December 31, 2020, zero shares issued and outstanding at March 31, 2021 and December 31, 2020
Common stock; $0.001 par value; 100,000,000 shares authorized at March 31, 2021 and December 31, 2020, 50,026,667 shares and 49,872,213 shares issued and outstanding at March 31, 2021 and December 31, 2020, respectively	50	50
Additional paid-in capital	646,015	641,195
Accumulated deficit	(415,618)	(392,317)
Accumulated other comprehensive income	12	73
Total stockholders' equity	230,459	249,001
Total liabilities and stockholders' equity	$ 250,228	$ 271,157