Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flow from operating activities
Net loss	$ (226,538)	$ (71,005)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	40,713	13,934
Depreciation and amortization	2,583	2,371
Amortization of right-of-use assets	1,701	552
Amortization of premiums on investments	2,804	(333)
Changes in operating assets and liabilities:
Receivable from collaboration partners ($326 and ($2,504) from a related party)	178	(2,447)
Prepaid expenses and other current assets	(5,290)	(6,906)
Other long-term assets	750	(1,373)
Accounts payable	(5,424)	3,165
Accrued research and development	19,163	23,665
Other accrued liabilities	5,082	2,485
Other current liabilities ($0 and $1,869 to a related party)		1,869
Deferred revenue (($23,133) and $193,140 to a related party)	(28,383)	187,890
Operating lease liabilities	(1,405)	(790)
Other long-term liabilities ($0 and $7,344 to a related party)	(2)	7,973
Net cash used in operating activities	(194,068)	161,050
Cash flow from investing activities
Purchases of short-term and long-term investments	(584,850)	(568,903)
Proceeds from maturities of short-term and long-term investments	572,140	135,300
Sales of short-term and long-term investments	7,500	1,003
Purchases of property and equipment	(17,572)	(1,536)
Net cash used in investing activities	(22,782)	(434,136)
Cash flow from financing activities
Proceeds from issuance of common stock ($220,235 and $164,207 from a related party)	220,235	433,776
Proceeds from issuance of common stock pursuant to equity award plans	5,440	3,271
Repurchase of unvested shares of stock	(6)	(49)
Net cash provided by financing activities	225,669	436,998
Net increase in cash and cash equivalents	8,819	163,912
Cash, cash equivalents and restricted cash at beginning of period	173,618	58,140
Cash, cash equivalents and restricted cash at end of period	182,437	222,052
Supplemental disclosures:
Cash paid for amounts included in measurement of lease liabilities	3,074	1,572
Cash received from tenant improvement allowances	792
Non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	24,473	13,004
Recognition of tenant improvement allowance receivable included in other current assets	10,598	979
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	4,605	245
Unpaid portion of other assets included in accrued research and development	3,000	0
Vesting of early exercised stock options and restricted stock	$ 529	643
Unpaid portion of financing costs included in accrued liabilities		$ 61