Fair Value Measurements, Cash Equivalents and Marketable Securities - Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Amortization cost, cash and cash equivalents	$ 215,169	$ 492,202	$ 938,590
Amortized cost, cash and cash equivalents and debt securities available-for-sale	1,166,542	1,499,957
Gross Unrealized Gain	0	2
Gross Unrealized Loss	(20,878)	(3,594)
Cash, cash equivalents and debt securities, fair value	1,145,664	1,496,365
Money market fund
Debt Securities, Available-for-sale [Line Items]
Amortization cost, cash and cash equivalents	124,569	357,785
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Estimated fair value, cash and cash equivalents	124,569	357,785
U.S. government debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost, debt securities, available-for-sale	1,041,973	1,142,172
Gross Unrealized Gain	0	2
Gross Unrealized Loss	(20,878)	(3,594)
Estimated fair value, debt securities	$ 1,021,095	$ 1,138,580