Investments (Analysis of Past Due Commercial Mortgage, Agricultural and Other Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	$ 1,508,259	$ 1,773,152
Non-Accrual Status	0	0
Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	1,457,959	1,668,578
Non-Accrual Status	0	0
Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	50,300	104,574
Non-Accrual Status	0	0
Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	1,457,959	1,668,578
Current
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	1,508,259	1,773,152
Current | Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	1,457,959	1,668,578
Current | Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	50,300	104,574
30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
30 to 59 Days Past Due | Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
30 to 59 Days Past Due | Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
60 to 89 Days Past Due | Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
60 to 89 Days Past Due | Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
90 Days or More Past Due | Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
90 Days or More Past Due | Agricultural Loan
Financing Receivable, Past Due [Line Items]
Recording investment gross of allowance for credit losses	0	0
90 Days or More Past Due | Loans
Financing Receivable, Past Due [Line Items]
Accruing Interest	$ 0	$ 0