Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flow from operating activities
Net loss	$ (148,563)	$ (72,827)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	26,128	7,932
Depreciation and amortization	1,620	1,629
Amortization of right-of-use assets	1,117	294
Amortization of premiums on investments	1,412	(323)
Changes in operating assets and liabilities:
Receivable from collaboration partners (($381) and $0 from a related party)	(526)	(90)
Prepaid expenses and other current assets	(9,086)	(4,601)
Other long-term assets	471	(135)
Accounts payable	(3,569)	6,668
Accrued research and development expenses	10,449	9,327
Other accrued liabilities	163	661
Deferred revenue (($15,422) and $0 to a related party)	(18,922)	(3,500)
Operating lease liabilities	(1,003)	(560)
Other long-term liabilities	(2)	310
Net cash used in operating activities	(140,311)	(55,215)
Cash flow from investing activities
Purchases of short-term and long-term investments	(370,690)	(139,689)
Proceeds from maturities of short-term and long-term investments	438,733	92,134
Sales of short-term and long-term investments	7,500	1,003
Purchases of property and equipment	(9,714)	(465)
Net cash provided by investing activities	65,829	(47,017)
Cash flow from financing activities
Proceeds from issuance of common stock ($220,235 and $56,738 from a related party)	220,235	326,512
Proceeds from issuance of common stock pursuant to equity award plans	4,122	3,001
Repurchase of unvested shares of stock	(6)	(33)
Net cash provided by financing activities	224,351	329,480
Net increase in cash and cash equivalents	149,869	227,248
Cash, cash equivalents and restricted cash at beginning of period	173,618	58,140
Cash, cash equivalents and restricted cash at end of period	323,487	285,388
Supplemental disclosures:
Cash paid for amounts included in measurement of lease liabilities	2,000	1,045
Non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	24,473	5,804
Tenant improvement allowance receivable included in other current assets	10,598
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	6,488	110
Vesting of early exercised stock options	$ 358	436
Unpaid portion of financing costs included in accounts payable		266
Unpaid portion of deferred financing costs included in accounts payable		$ 316