Investments - Available-for-sale securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale
Proceeds from sales and maturities of available-for-sale securities	$ 1,400,000
Amortized Cost		$ 1,355,614
Gross Unrealized Gains		118
Gross Unrealized Losses		(22,789)
Fair Value	$ 0	1,332,943
Corporate bonds
Debt Securities, Available-for-sale
Amortized Cost		200,735
Gross Unrealized Gains		7
Gross Unrealized Losses		(7,109)
Fair Value		193,633
U.S. Treasuries
Debt Securities, Available-for-sale
Amortized Cost		1,154,879
Gross Unrealized Gains		111
Gross Unrealized Losses		(15,680)
Fair Value		$ 1,139,310