Fair Value Measurements - Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	$ 414,411
Unrealized Losses within 12 months, Unrealized Losses	(396)
Unrealized Losses 12 months or greater, Fair Value	332,655
Unrealized Losses 12 months or greater, Unrealized Losses	(301)
Total, Fair Value	747,066
Total, Unrealized Losses	(697)
U.S. government notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	62,724
Unrealized Losses within 12 months, Unrealized Losses	(74)
Unrealized Losses 12 months or greater, Fair Value	127,869
Unrealized Losses 12 months or greater, Unrealized Losses	(146)
Total, Fair Value	190,593
Total, Unrealized Losses	(220)
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	221,914
Unrealized Losses within 12 months, Unrealized Losses	(133)
Unrealized Losses 12 months or greater, Fair Value	101,990
Unrealized Losses 12 months or greater, Unrealized Losses	(114)
Total, Fair Value	323,904
Total, Unrealized Losses	(247)
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	129,773
Unrealized Losses within 12 months, Unrealized Losses	(189)
Unrealized Losses 12 months or greater, Fair Value	102,796
Unrealized Losses 12 months or greater, Unrealized Losses	(41)
Total, Fair Value	232,569
Total, Unrealized Losses	$ (230)