Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (234,632)	$ (183,118)	$ (250,219)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	47,084	81,924	62,201
Depreciation and amortization expense	20,250	18,020	13,624
Impairment of other investments	12,923	5,000	36,447
Net amortization and accretion on marketable securities	(9,596)	(930)	1,901
Change in fair value of success payment liabilities	(2,780)	(5,130)	3,713
Non-cash lease (income) expense	(1,873)	(1,553)	911
Loss on property and equipment disposals, net	1,509	103	1,210
Change in fair value of equity warrant	0	1,067	256
Gain on other investments	0	(2,923)	0
Gain on net operating lease liability disposal	0	0	(308)
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and other assets	3,125	(1,968)	(6,987)
Accounts payable	1,464	667	91
Accrued liabilities and other current liabilities	(719)	(463)	4,542
Deferred revenue	0	(84,653)	(10,508)
Operating lease liabilities, non-current	0	4,855	13,202
Other non-current liabilities	(449)	(453)	3,675
Net cash used in operating activities	(163,694)	(169,555)	(126,249)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(2,686)	(24,276)	(65,504)
Purchases of marketable securities	(476,880)	(406,316)	(673,465)
Sales and maturities of marketable securities	663,614	419,052	617,396
Net cash provided by (used in) investing activities	184,048	(11,540)	(121,573)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercise of stock options	306	9,577	9,442
Proceeds from employee stock purchase plan	1,894	1,519	0
Taxes paid related to net share settlement of equity awards	(457)	(461)	0
Proceeds from initial public offering, net of issuance costs	0	0	391,802
Net cash provided by financing activities	1,743	10,635	401,244
Net increase (decrease) in cash, cash equivalents and restricted cash	22,097	(170,460)	153,422
Cash, cash equivalents and restricted cash at beginning of period	123,834	294,294	140,872
Cash, cash equivalents and restricted cash at end of period	145,931	123,834	294,294
Represented by:
Cash and cash equivalents	145,647	123,554	293,828
Restricted cash	284	280	466
Total	145,931	123,834	294,294
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid for amounts included in the measurement of lease liabilities	10,845	10,870	8,546
Cash received for amounts related to tenant improvement allowances	0	4,761	13,295
Non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued liabilities	29	1,325	4,605
Remeasurement of operating lease right-of-use asset for lease modification	0	31	3,873
Acquisition of PACT Series D convertible preferred shares	0	2,923	0
Conversion of convertible preferred stock to common stock upon closing of initial public offering	$ 0	$ 0	$ 1,010,968