CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net loss	$ (418,259)	$ (132,694)	$ (184,748)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	4,885	5,676	8,159
Gain on sale of assets	0	(9,016)	0
Non-cash impact of lease termination	0	0	(4,381)
Amortization of debt issuance costs	1,424	1,424	1,424
Right-of-use assets expensed	245,861	0	0
Non-cash stock-based compensation	128,035	17,048	18,314
Other	(16,504)	4,957	(2,451)
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other assets	(422,689)	(4,202)	1,212
Accounts payable and accrued expenses	163,161	(11,485)	(6,744)
Deferred revenue	271,545	(8,331)	(15,610)
Net cash used in operating activities	(42,541)	(136,623)	(184,825)
Investing Activities:
Capital expenditures	(54,622)	(1,857)	(1,372)
Acquisition of Novavax CZ, net of cash acquired	(165,516)	0	0
Proceeds from sale of assets	0	18,333	0
Purchases of marketable securities	(363,202)	(17,484)	(120,150)
Proceeds from maturities of marketable securities	205,562	39,500	150,118
Net cash (used in) provided by investing activities	(377,778)	38,492	28,596
Financing Activities:
Proceeds from issuance of preferred stock	199,822	0	0
Net proceeds from sales of common stock	875,623	97,392	100,060
Proceeds from the exercise of stock-based awards	44,469	992	2,745
Treasury stock related to tax withholding on stock-based awards	(39,087)	0	0
Finance lease payments	(96,065)	0	0
Net cash provided by financing activities	984,762	98,384	102,805
Effect of exchange rate on cash, cash equivalents and restricted cash	2,115	(32)	(48)
Net increase (decrease) in cash, cash equivalents and restricted cash	566,558	221	(53,472)
Cash, cash equivalents and restricted cash at beginning of year	82,180	81,959	135,431
Cash, cash equivalents and restricted cash at end of year	648,738	82,180	81,959
Supplemental disclosure of non-cash activities:
Sale of common stock under the Sales Agreement not settled at year-end	3,227	497	0
Capital expenditures included in accounts payable and accrued expenses	9,255	49	519
Right-of-use assets from new lease agreements	247,599	0	0
Supplemental disclosure of cash flow information:
Cash interest payments, net of amounts capitalized	$ 13,705	$ 12,188	$ 12,188