Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (193,016)	$ (110,912)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,185	2,435
Amortization of intangible assets	918	918
Impairment of intangible assets	832
Amortization of premiums (accretion of discounts) on investments, net	1,052	(571)
Noncash lease expense	2,498
Change in estimated fair value of contingent consideration	44,432	819
Payment of contingent consideration in excess of acquisition date fair value	(6,453)
Change in estimated fair value of derivative liability	16,796
Change in estimated fair value of convertible preferred stock warrant liability		3,401
Common stock issued in connection with license agreement		617
Stock-based compensation	17,299	6,040
Other	17
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(416)	(109)
Other assets	(2,168)	(1,399)
Accounts payable	1,041	428
Accrued liabilities and other long-term liabilities	13,183	5,678
Operating lease liabilities	(2,343)
Deferred revenue	(5,746)	1,908
Net cash used in operating activities	(108,889)	(90,747)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(4,119)	(7,388)
Purchases of investments	(363,399)	(495,934)
Maturities of investments	296,763	320,933
Proceeds from disposal of an asset held for sale	180
Net cash used in investing activities	(70,575)	(182,389)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	323,214
Proceeds from issuance of convertible preferred stock, net of issuance costs		317,335
Payment of contingent consideration	(3,547)
Proceeds received from financing lease obligation		1,202
Payment of principal on financing lease obligation	(173)	(38)
Payment of offering costs related to initial public offering		(3,686)
Proceeds from repayment of promissory notes		3,265
Proceeds from exercise of stock options	3,540	1,066
Net cash provided by financing activities	529,733	319,144
Net increase in cash, cash equivalents and restricted cash and cash equivalents	350,269	46,008
Cash, cash equivalents and restricted cash and cash equivalents at beginning of period	122,816	59,362
Cash, cash equivalents and restricted cash and cash equivalents at end of period	473,085	105,370
NONCASH INVESTING AND FINANCING ACTIVITIES:
Property and equipment purchases included in accounts payable and accrued liabilities	598	200
Reclassification of derivative liability to additional paid-in capital	29,245
Operating lease liabilities obtained in exchange of right-of-use asset	437
Deferred offering costs in accounts payable and accrued liabilities		1,938
Advanced proceeds applied to convertible preferred stock issuance		10,140
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH TO THE CONDENSED CONSOLIDATED BALANCE SHEETS:
Cash and cash equivalents	462,521	93,698
Restricted cash and cash equivalents, current	9,363	8,822
Restricted cash and cash equivalents, noncurrent	1,201	2,850
Cash, cash equivalents and restricted cash and cash equivalents at end of period	473,085	$ 105,370
Collaboration Agreement
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	$ 206,699