Investments (Analysis of Past Due Commercial Mortgage, Agricultural and Other Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	$ 8,709,931	$ 7,797,038
Non-Accrual Status	42,845	29,885
Current
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	8,672,643	7,767,876
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	2,505
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	37,288	26,657
Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	7,807,466	6,955,018
Non-Accrual Status	5,120	5,120
Commercial mortgage loans | Current
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	7,803,543	6,951,093
Commercial mortgage loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Commercial mortgage loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Commercial mortgage loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	3,923	3,925
Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	891,999	830,041
Non-Accrual Status	37,725	24,765
Agricultural Loan | Current
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	858,634	804,804
Agricultural Loan | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Agricultural Loan | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	2,505
Agricultural Loan | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	33,365	22,732
Other Collateralized Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	10,466	11,979
Non-Accrual Status	0	0
Other Collateralized Loans | Current
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	10,466	11,979
Other Collateralized Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Other Collateralized Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Other Collateralized Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Accruing Interest	$ 0	$ 0