Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (191,163)	$ (133,299)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	46,768	5,714
Noncash licensing expense		100
Depreciation and amortization	105	72
Amortization of premium on investment securities	(75)	(209)
Amortization of debt issuance costs	694	539
Amortization of leasehold interest	163	137
Noncash change in lease liability and right-of-use asset	1,364	1,921
Change in fair value of notes payable	286	28
Changes in assets and liabilities:
Decrease in other current assets	2,398	2,226
Decrease in accrued interest receivable	105
Increase (decrease) in accounts payable and accrued expenses	5,893	(3,837)
Decrease in lease liabilities	(1,360)	(1,129)
Increase in interest payable	238	787
(Decrease) increase in other liabilities	(27,783)	24,651
Decrease in deferred revenue	(114)	(114)
Net cash used in operating activities	(162,481)	(102,413)
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from maturity of short-term securities	35,250	22,500
Investment in short-term securities		(23,125)
Investment in held-to-maturity securities	(7,482)
Purchases of equipment	(202)	(97)
Net cash provided by (used in) investing activities	27,566	(722)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from sale of common stock, net	276,303	76,664
Proceeds from exercise of options	135
Proceeds from debt financings		29,675
Financing costs paid		(480)
Net cash provided by financing activities	276,438	105,859
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	141,523	2,724
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	113,888	43,199
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	$ 255,411	$ 45,923