Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 195,245
Due after one year through five years	910,005
Due after five years through 10 years	567,327
Due after 10 years	573,985
ABS/CMBS/MBS	700,358
Total available-for-sale	2,946,920	$ 2,945,273
Fair Value
Due in one year or less	193,554
Due after one year through five years	861,351
Due after five years through 10 years	529,864
Due after 10 years	479,971
ABS/CMBS/MBS	624,360
Total available-for-sale	$ 2,689,100	$ 2,666,950