Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 242,522
Due after one year through five years	847,005
Due after five years through 10 years	775,964
Due after 10 years	548,359
ABS/CMBS/MBS	804,016
Total available-for-sale	3,217,866	$ 3,054,391
Fair Value
Due in one year or less	239,183
Due after one year through five years	815,300
Due after five years through 10 years	745,887
Due after 10 years	454,421
ABS/CMBS/MBS	734,736
Total available-for-sale	$ 2,989,527	$ 2,855,849