Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (90,628)	$ (51,116)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	16,618	11,068
Depreciation and amortization	59	30
Amortization of premium on investment securities	127
Amortization of premium on investment securities		(44)
Amortization of debt issuance costs	231	231
Amortization of leasehold interest	53	54
Noncash change in lease liability and right of use asset	479	2,001
Change in fair value of notes payable	(58)	(20)
Changes in assets and liabilities:
Increase in other current assets	(4,107)	(1,017)
Increase in accounts receivable	(771)
Increase (decrease) in accounts payable and accrued expenses	904	(1,567)
Decrease in lease liabilities	(507)	(1,967)
Decrease in other liabilities	(3,717)	(19,730)
Decrease in deferred revenue	(38)	(38)
Net cash used in operating activities	(81,355)	(62,115)
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from maturity of short-term securities	17,000	9,000
Investment in held-to-maturity securities	(17,447)	(7,482)
Purchases of equipment	(67)	(68)
Net cash (used in) provided by investing activities	(514)	1,450
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercise of options	128	81
Offering costs paid	(183)
Net cash (used in) provided by financing activities	(55)	81
NET DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(81,924)	(60,584)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	554,698	113,887
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	$ 472,774	$ 53,303