Investments (Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 6,315,566	$ 6,155,050
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for Credit Losses	$ (42,682)	$ (37,689)
Commercial Mortgage Loans	6,279,862	6,122,721
Total net Commercial Mortgage and Other Loans	6,279,862	6,122,721
Other loans	6,978	5,360
Commercial Mortgage and Agricultural Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial Mortgage Loans	6,272,884	6,117,361
Total net Commercial Mortgage and Other Loans	6,272,884	6,117,361
Other Collateralized Loans
Commercial Mortgage and Other Loans [Line Items]
Other loans	6,978	5,360
Total Net Commercial Mortgage and Other Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial Mortgage Loans	6,279,862	6,122,721
Total net Commercial Mortgage and Other Loans	6,279,862	6,122,721
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 1,640,502	$ 1,578,785
Commercial mortgage loans, Percentage	26.00%	25.70%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 102,388	$ 102,952
Commercial mortgage loans, Percentage	1.60%	1.70%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 2,390,837	$ 2,486,230
Commercial mortgage loans, Percentage	37.90%	40.40%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 593,748	$ 604,611
Commercial mortgage loans, Percentage	9.40%	9.80%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 660,992	$ 456,720
Commercial mortgage loans, Percentage	10.50%	7.40%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 351,806	$ 363,706
Commercial mortgage loans, Percentage	5.50%	5.90%
Commercial mortgage loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 5,740,273	$ 5,593,004
Commercial mortgage loans, Percentage	90.90%	90.90%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans	$ 575,293	$ 562,046
Commercial mortgage loans, Percentage	9.10%	9.10%