Investments - Schedule of Amortized Cost and Fair Value of Investments in Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Debt Securities Available for Sale, Amortized Cost
Due in 1 year or less	$ 719,108
Due after 1 year through 5 years	2,866,915
Due after 5 years through 10 years	1,812,394
Due after 10 years	2,046,372
Total, excluding mortgage and asset-backed securities	7,444,789
Mortgage and asset-backed securities	993,971
Total before allowance for credit losses	8,438,760	$ 8,604,250
Allowance for credit losses	0	0	$ 0
Total	8,438,760
Debt Securities Available for Sale, Fair Value
Due in 1 year or less	714,084
Due after 1 year through 5 years	2,747,445
Due after 5 years through 10 years	1,625,461
Due after 10 years	1,640,459
Total, excluding mortgage and asset-backed securities	6,727,449
Mortgage and asset-backed securities	884,184
Total	7,611,633	$ 9,068,946
Allowance for credit losses	$ 0