Investments (Amortized Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available-for-sale, Amortized Cost
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One	$ 500
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five	14,026
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	60,829
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	72,509
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost	75,355
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	623,366
Amortized Cost	796,960	$ 1,508,981
Available-for-sale, Fair Value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One	500
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five	12,526
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	59,483
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10	0
Total	695,875	$ 1,507,486
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	$ 721,605