Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 48,305
Due after one year through five years	790,904
Due after five years through 10 years	516,860
Due after 10 years	514,144
ABS/CMBS/MBS	610,267
Total available-for-sale	2,480,480	$ 2,346,267
Fair Value
Due in one year or less	48,372
Due after one year through five years	765,266
Due after five years through 10 years	477,956
Due after 10 years	430,249
ABS/CMBS/MBS	559,066
Total available-for-sale	$ 2,280,909	$ 2,409,887