Fair Value Measurements. Cash Equivalents and Marketable Securities - Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortization cost, cash and cash equivalents	$ 1,133,537	$ 141,647	$ 492,202
Amortized cost, cash and cash equivalents and debt securities available-for-sale	1,067,608	904,446
Gross Unrealized Gain	0	8
Gross Unrealized Loss	(11)	(16,779)
Cash, cash equivalents and debt securities, fair value	1,067,597	887,675
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortization cost, cash and cash equivalents	1,032,500	3,104
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Estimated fair value, cash and cash equivalents	1,032,500	3,104
U.S. government debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost, debt securities, available-for-sale	35,108	901,342
Gross Unrealized Gain	0	8
Gross Unrealized Loss	(11)	(16,779)
Estimated fair value, debt securities	$ 35,097	$ 884,571