Fair Value Measurements - Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	$ 2,298,926
Unrealized Losses within 12 months, Unrealized Losses	(13,479)
Unrealized Losses 12 months or greater, Fair Value	132,590
Unrealized Losses 12 months or greater, Unrealized Losses	(46)
Total, Fair Value	2,431,516
Total, Unrealized Losses	(13,525)
U.S. government notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	771,014
Unrealized Losses within 12 months, Unrealized Losses	(4,598)
Unrealized Losses 12 months or greater, Fair Value	61,043
Unrealized Losses 12 months or greater, Unrealized Losses	(18)
Total, Fair Value	832,057
Total, Unrealized Losses	(4,616)
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	1,027,448
Unrealized Losses within 12 months, Unrealized Losses	(6,463)
Unrealized Losses 12 months or greater, Fair Value	62,047
Unrealized Losses 12 months or greater, Unrealized Losses	(28)
Total, Fair Value	1,089,495
Total, Unrealized Losses	(6,491)
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	500,464
Unrealized Losses within 12 months, Unrealized Losses	(2,418)
Unrealized Losses 12 months or greater, Fair Value	9,500
Unrealized Losses 12 months or greater, Unrealized Losses	0
Total, Fair Value	509,964
Total, Unrealized Losses	$ (2,418)