Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 899,250	$ 1,661,082
Marketable securities	1,104,767	438,467
Prepaid expenses and other current assets	23,083	22,821
Collaboration receivable - related party	24,766
Total current assets	2,051,866	2,122,370
Property and equipment, net	4,173	6,755
Restricted cash	1,269	1,716
Right-of-use operating asset	19,998	25,064
Other long-term assets	3,392	3,341
Total assets	2,080,698	2,159,246
Current liabilities:
Accounts payable	3,285	3,691
Accrued expenses	51,420	54,851
Operating lease liability, current portion	7,306	8,662
Total current liabilities	62,011	67,204
Operating lease liability, net of current portion	15,411	19,438
Other liabilities		270
Total liabilities	77,422	86,912
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at March 31, 2021 and December 31, 2020; no shares issued or outstanding at March 31, 2021 and December 31, 2020
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at March 31, 2021 and December 31, 2020; 58,409,854 and 58,311,444 shares issued at March 31, 2021 and December 31, 2020; 58,406,821 and 58,308,411 shares outstanding at March 31, 2021 and December 31, 2020	6	6
Treasury stock, at cost, 3,033 shares at March 31, 2021 and December 31, 2020	(400)	(400)
Additional paid-in capital	3,137,164	3,109,807
Accumulated deficit	(1,133,258)	(1,037,494)
Accumulated other comprehensive gain (loss)	(236)	415
Total stockholders’ equity	2,003,276	2,072,334
Total liabilities and stockholders’ equity	$ 2,080,698	$ 2,159,246