Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 22,335	$ 31,683
Marketable securities	132,841	149,242
Income tax receivable	697	1,507
Other receivables	305	557
Prepaid expenses	8,295	12,076
Total current assets	164,473	195,065
Operating lease right-of-use assets	3,641	4,279
Marketable securities, non-current	52,216	70,565
Property and equipment, net	716	840
Restricted cash	408	408
Total assets	221,454	271,157
Current liabilities:
Accounts payable and accrued expenses	13,493	16,881
Operating lease liabilities, current	1,677	1,602
Total current liabilities	15,170	18,483
Operating lease liabilities, non-current	2,818	3,673
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at June 30, 2021 and December 31, 2020, zero shares issued and outstanding at June 30, 2021 and December 31, 2020
Common stock; $0.001 par value; 100,000,000 shares authorized at June 30, 2021 and December 31, 2020, 50,088,161 shares and 49,872,213 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	50	50
Additional paid-in capital	649,784	641,195
Accumulated deficit	(446,363)	(392,317)
Accumulated other comprehensive (loss) income	(5)	73
Total stockholders' equity	203,466	249,001
Total liabilities and stockholders' equity	$ 221,454	$ 271,157