Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 110,703	$ 49,969
Marketable securities	252,041	363,339
Prepaid expenses and other current assets	11,993	8,203
Total current assets	374,737	421,511
Property and equipment, net	29,469	30,181
Operating lease right-of-use assets	32,094	32,470
Restricted cash	1,472	1,472
Other assets	2,592	2,617
Total assets	440,364	488,251
Current liabilities:
Accounts payable	5,310	3,004
Accrued clinical supply costs	9,384	11,148
Accrued liabilities	18,970	22,538
Deferred revenue, current portion	22,700	23,886
Operating lease liabilities, current portion	7,698	7,512
Total current liabilities	64,062	68,088
Deferred revenue, long-term portion	105,493	108,417
Operating lease liabilities, long-term portion	42,822	43,744
Other long-term liabilities	158	472
Total liabilities	212,535	220,721
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 79,731,647 and 79,316,261 shares issued and outstanding as of March 31, 2021 and December 31, 2020	8	8
Additional paid-in capital	689,630	676,956
Accumulated other comprehensive income	410	614
Accumulated deficit	(462,219)	(410,048)
Total stockholders' equity	227,829	267,530
Total liabilities and stockholders’ equity	$ 440,364	$ 488,251