Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 44,732
Due after one year through five years	667,555
Due after five years through 10 years	533,651
Due after 10 years	506,651
ABS/CMBS/MBS	621,667
Total available-for-sale	2,374,256	$ 2,346,267
Fair Value
Due in one year or less	45,069
Due after one year through five years	660,532
Due after five years through 10 years	521,300
Due after 10 years	471,714
ABS/CMBS/MBS	593,763
Total available-for-sale	$ 2,292,378	$ 2,409,887