Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 332,951
Due after one year through five years	916,676
Due after five years through 10 years	522,104
Due after 10 years	523,729
ABS/CMBS/MBS	649,813
Total available-for-sale	2,945,273	$ 2,346,267
Fair Value
Due in one year or less	331,761
Due after one year through five years	873,530
Due after five years through 10 years	474,025
Due after 10 years	415,092
ABS/CMBS/MBS	572,542
Total available-for-sale	$ 2,666,950	$ 2,409,887