Investments - Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Amortized Cost	$ 5,776,666
Loaned securities	149,541	$ 112,139
Fixed-maturities available for sale, amortized cost	5,683,372	5,587,261
Fair Value
Fair Value	5,116,509
Loaned securities	149,541	112,139
Total fixed-maturities available for sale, Fair Value	5,037,747	5,017,711
Non asset-backed securities
Amortized Cost
Due in one year or less	108,051
Due after one year through five years	1,296,150
Due after five years through 10 years	917,687
Due after 10 years	866,821
Fair Value
Due in one year or less	106,300
Due after one year through five years	1,209,013
Due after five years through 10 years	781,903
Due after 10 years	635,284
Asset-backed and mortgage-backed securities
Amortized Cost
Asset-backed and mortgage-backed securities	2,587,957
Fair Value
Asset-backed and mortgage-backed securities	2,384,009
Total fixed-maturities available for sale
Amortized Cost
Fixed-maturities available for sale, amortized cost	5,683,372	5,587,261
Fair Value
Total fixed-maturities available for sale, Fair Value	5,037,747	$ 5,017,711
Loaned securities, amortized cost
Amortized Cost
Loaned securities	93,294
Fair Value
Loaned securities	93,294
Loaned securities, fair value
Amortized Cost
Loaned securities	78,762
Fair Value
Loaned securities	$ 78,762

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