Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 207,537	$ 79,449
Short-term marketable securities	379,713	335,907
Prepaid expenses and other current assets	17,535	14,675
Total current assets	604,785	430,031
Long-term marketable securities	9,684	39,886
Property and equipment, net	45,452	46,732
Operating lease right-of-use asset	33,626	33,923
Other non-current assets	2,318	2,659
Total assets	695,865	553,231
Current liabilities:
Accounts payable	2,316	2,590
Accrued compensation	3,910	8,739
Accrued clinical costs	5,349	5,042
Other accruals and other current liabilities	7,265	6,569
Operating lease liability, current	4,121	3,665
Contract liabilities	24,674	18,739
Total current liabilities	47,635	45,344
Contract liabilities, less current portion	34,747	43,753
Operating lease liability, less current portion	67,793	68,865
Other non-current liabilities	379	379
Total liabilities	150,554	158,341
Commitments and contingencies (Note 8)
Stockholders' equity:
Convertible preferred stock, $0.01 par value; 40,000,000 shares authorized as of March 31, 2020 and December 31, 2019; 0 shares issued and outstanding as of March 31, 2020 and December 31, 2019	0	0
Common stock, $0.01 par value; 400,000,000 shares authorized as of March 31, 2020 and December 31, 2019; 105,541,343 shares and 96,189,935 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively	1,382	1,288
Additional paid-in capital	1,025,408	818,803
Accumulated other comprehensive income	835	350
Accumulated deficit	(482,314)	(425,551)
Total stockholders' equity	545,311	394,890
Total liabilities and stockholders’ equity	$ 695,865	$ 553,231