Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 137,184	$ 79,449
Short-term marketable securities	412,397	335,907
Prepaid expenses and other current assets	9,828	14,675
Total current assets	559,409	430,031
Long-term marketable securities	7,229	39,886
Property and equipment, net	43,622	46,732
Operating lease right-of-use asset	33,312	33,923
Other non-current assets	3,765	2,659
Total assets	647,337	553,231
Current liabilities:
Accounts payable	1,866	2,590
Accrued compensation	5,531	8,739
Accrued clinical costs	4,179	5,042
Other accruals and other current liabilities	8,424	6,569
Operating lease liability, current	4,330	3,665
Contract liabilities	34,134	18,739
Total current liabilities	58,464	45,344
Contract liabilities, less current portion	19,715	43,753
Operating lease liability, less current portion	66,612	68,865
Other non-current liabilities	379	379
Total liabilities	145,170	158,341
Commitments and contingencies (Note 8)
Stockholders' equity:
Convertible preferred stock, $0.01 par value; 40,000,000 shares authorized as of June 30, 2020 and December 31, 2019; 0 shares issued and outstanding as of June 30, 2020 and December 31, 2019	0	0
Common stock, $0.01 par value; 400,000,000 shares authorized as of June 30, 2020 and December 31, 2019; 105,897,872 shares and 96,189,935 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	1,385	1,288
Additional paid-in capital	1,041,303	818,803
Accumulated other comprehensive income	551	350
Accumulated deficit	(541,072)	(425,551)
Total stockholders' equity	502,167	394,890
Total liabilities and stockholders’ equity	$ 647,337	$ 553,231