Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (250,219)	$ (204,472)	$ (129,377)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Stock-based compensation expense	62,201	33,261	15,732
Impairment of other investments	36,447	0	0
Depreciation and amortization	13,624	4,294	1,256
Change in fair value of success payment liabilities	3,713	5,337	436
Change in fair value of warrants	256	(1,323)	0
Lease expense, net of gain on lease remeasurement	911	3,181	3,127
Non-cash expense in connection with asset acquisition	0	3,529	0
Net amortization or accretion on marketable securities	1,901	539	(1,518)
Loss on remeasurement of convertible preferred stock tranche liabilities	0	0	35,444
Expense in connection with equity issuances	0	0	3,566
Loss (gain) on property and equipment disposals	1,210	(4,884)	0
Gain on net operating lease liability disposal	(308)	0	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(6,987)	(1,388)	(5,767)
Accounts payable	91	(278)	1,709
Accrued liabilities and other current liabilities	4,542	6,120	9,755
Deferred revenue	(10,508)	(7,756)	102,917
Operating lease liabilities, non-current	13,202	2,966	2,194
Other non-current liabilities	3,675	0	0
Net cash (used in) provided by operating activities	(126,249)	(160,874)	39,474
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(65,504)	(51,481)	(16,047)
Purchases of marketable securities	(673,465)	(864,909)	(610,842)
Sales and maturities of marketable securities	617,396	686,322	238,456
Purchases of other investments	0	(43,448)	(34,000)
Net cash used in investing activities	(121,573)	(273,516)	(422,433)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from initial public offering, net of issuance costs	391,802	0	0
Proceeds from issuance of convertible preferred stock, net of issuance costs	0	492,467	351,341
Proceeds from exercise of stock options	9,442	373	0
Payments for the repurchase of common stock	0	(11,806)	(185)
Payments for the repurchase of convertible preferred stock	0	(4,244)	0
Net cash provided by financing activities	401,244	476,790	351,156
Net increase (decrease) in cash, cash equivalents and restricted cash	153,422	42,400	(31,803)
Cash, cash equivalents and restricted cash at beginning of period	140,872	98,472	130,275
Cash, cash equivalents and restricted cash at end of period	294,294	140,872	98,472
Represented by:
Cash and cash equivalents	293,828	140,406	96,674
Restricted cash	466	466	1,798
Total	294,294	140,872	98,472
SUPPLEMENTAL CASH FLOW INFORMATION
Cash received for amounts related to tenant improvement allowances	13,295	2,966	2,194
Cash paid for amounts included in the measurement of lease liabilities	8,546	5,147	1,464
Non-cash investing and financing activities:
Conversion of convertible preferred stock to common stock upon closing of initial public offering	1,010,968	0	0
Purchases of property and equipment included in accounts payable and accrued liabilities	4,605	12,740	3,185
Operating lease right-of-use assets obtained in exchange for lease obligations	0	30,475	23,656
Remeasurement of operating lease right-of-use asset for lease modification	3,873	(8,958)	0
Other investments received for sale of assets	0	6,000	0
Non-cash deemed dividends on convertible preferred stock	$ 0	$ 0	$ 1,144