Investments (Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 5,519,969	$ 4,948,943
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for Credit Losses	$ (27,100)	$ (20,263)
Commercial Mortgage Loans	5,492,869	4,928,680
Commercial Mortgage and Agricultural Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial Mortgage Loans	5,492,869	4,928,680
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 1,450,305	$ 1,289,026
Commercial mortgage loans, Percentage	26.30%	26.00%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 102,536	$ 104,177
Commercial mortgage loans, Percentage	1.90%	2.10%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 2,097,019	$ 1,766,247
Commercial mortgage loans, Percentage	38.00%	35.80%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 580,189	$ 590,897
Commercial mortgage loans, Percentage	10.50%	11.90%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 410,324	$ 380,121
Commercial mortgage loans, Percentage	7.40%	7.70%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 364,678	$ 351,457
Commercial mortgage loans, Percentage	6.60%	7.10%
Commercial mortgage loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 5,005,051	$ 4,481,925
Commercial mortgage loans, Percentage	90.70%	90.60%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 514,918	$ 467,018
Commercial mortgage loans, Percentage	9.30%	9.40%