Investments (Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 8,081,694	$ 7,785,059
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for Credit Losses	$ (39,784)	$ (37,715)
Commercial Mortgage Loans	8,054,419	7,759,323
Total net Commercial Mortgage and Other Loans	8,054,419	7,759,323
Other loans	12,509	11,979
Commercial Mortgage and Agricultural Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial Mortgage Loans	8,041,910	7,747,344
Total net Commercial Mortgage and Other Loans	8,041,910	7,747,344
Other Collateralized Loans
Commercial Mortgage and Other Loans [Line Items]
Other loans	12,509	11,979
Total Net Commercial Mortgage and Other Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial Mortgage Loans	8,054,419	7,759,323
Total net Commercial Mortgage and Other Loans	8,054,419	7,759,323
Apartments/Multi-Family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 2,070,419	$ 1,949,926
Commercial mortgage loans, Percentage	25.60%	25.00%
Health Care Senior Living
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 133,731	$ 134,195
Commercial mortgage loans, Percentage	1.70%	1.70%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 95,008	$ 97,603
Commercial mortgage loans, Percentage	1.20%	1.30%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 3,014,351	$ 2,906,413
Commercial mortgage loans, Percentage	37.30%	37.30%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 545,065	$ 556,586
Commercial mortgage loans, Percentage	6.70%	7.10%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 693,519	$ 693,949
Commercial mortgage loans, Percentage	8.60%	9.00%
Self-Storage
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 598,911	$ 543,701
Commercial mortgage loans, Percentage	7.40%	7.00%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 72,554	$ 72,645
Commercial mortgage loans, Percentage	0.90%	0.90%
Total commercial mortgage loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 7,223,558	$ 6,955,018
Commercial mortgage loans, Percentage	89.40%	89.30%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 858,136	$ 830,041
Commercial mortgage loans, Percentage	10.60%	10.70%