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	$ (76,161)	$ (80,789)
Adjustments to reconcile net loss to net cash provided by operating activities:
Stock-based compensation expense	29,313	13,715
Depreciation and amortization expense	1,613	876
Amortization of premium on investments	(164)	(3,179)
Non-cash lease expense	5,533	1,387
Changes in operating assets and liabilities:
Litigation settlement payable	0	(10,500)
Deferred revenue	73,555	(5,550)
Prepaid expenses and other assets	(12,431)	(6,311)
Accounts payable	1,396	191
Contract receivables	195,326	97,000
Accrued expenses and other liabilities	10,104	8,840
Lease liability	(6,132)	(1,448)
Deferred charges and other assets	463	0
Net cash provided by operating activities	222,415	14,232
CASH FLOWS FROM INVESTING ACTIVITIES:
Maturities of held-to-maturity investments	420,000	306,000
Purchases of held-to-maturity investments	(629,403)	(319,919)
Purchases of property and equipment	(7,494)	(5,314)
Other	15	0
Net cash used in investing activities	(216,882)	(19,233)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of placement agent commissions	39,192	0
Payments of common stock offering costs	(104)	(50)
Proceeds from exercises of stock options and issuances under Employee Stock Purchase Plan	9,346	842
Other	(34)	0
Net cash provided by financing activities	48,400	792
Effect of exchange rate changes on cash, cash equivalents, and restricted cash equivalents	0	(4)
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH EQUIVALENTS	53,933	(4,213)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH EQUIVALENTS – Beginning of period	156,710	54,983
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH EQUIVALENTS – End of period	210,643	50,770
NONCASH OPERATING ACTIVITIES
Right-of-use assets acquired through operating leases	1,101	667
NONCASH INVESTING ACTIVITIES
Property and equipment purchases included in accounts payable and accrued expenses	568	0
NONCASH FINANCING ACTIVITIES
Right-of-use assets acquired through financing leases	48	0
Total cash, cash equivalents, and restricted cash equivalents shown in the condensed consolidated statements of cash flows	$ 210,643	$ 50,770