Investments - Schedule of Amortized Cost and Fair Value of Investments In Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Securities Available for Sale, Amortized Cost
Due in 1 year or less	$ 256,576
Due after 1 year through 5 years	3,198,107
Due after 5 years through 10 years	2,205,479
Due after 10 years	1,995,736
Total, excluding mortgage and asset-backed securities	7,655,898
Mortgage and asset-backed securities	948,352
Total before allowance for credit losses	8,604,250	$ 9,874,543
Allowance for Credit Losses	0	0	$ 0
Total	8,604,250
Debt Securities Available for Sale, Fair Value
Due in 1 year or less	258,754
Due after 1 year through 5 years	3,353,853
Due after 5 years through 10 years	2,355,857
Due after 10 years	2,132,842
Total, excluding mortgage and asset-backed securities	8,101,306
Mortgage and asset-backed securities	967,640
Total	9,068,946	$ 10,770,923
Allowance for credit losses	$ 0