Investments - Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Debt Securities Available for Sale - Amortized Cost
Due in 1 year or less	$ 188,676
Due after 1 year through 5 years	3,121,279
Due after 5 years through 10 years	2,232,161
Due after 10 years	2,229,963
Amortized Cost	7,772,079
Mortgage and asset-backed securities	1,037,515
Totals before allowance for credit losses	8,809,594	$ 8,604,250
Allowance for Credit Losses	0	0	$ 0	$ 0
Totals	8,809,594
Debt Securities Available for Sale - Fair Value
Due in 1 year or less	189,234
Due after 1 year through 5 years	3,155,586
Due after 5 years through 10 years	2,217,928
Due after 10 years	2,140,804
Fair Value	7,703,552
Mortgage and asset-backed securities	1,012,322
Allowance for credit losses	0
Total	$ 8,715,874	$ 9,068,946