Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 294,528
Due after one year through five years	904,163
Due after five years through 10 years	514,187
Due after 10 years	546,390
ABS/CMBS/MBS	674,045
Total available-for-sale	2,933,313	$ 2,945,273
Fair Value
Due in one year or less	293,229
Due after one year through five years	865,507
Due after five years through 10 years	478,924
Due after 10 years	457,798
ABS/CMBS/MBS	606,356
Total available-for-sale	$ 2,701,814	$ 2,666,950