Investments (Analysis of Past Due Commercial Mortgage, Agricultural and Other Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 1,645,692	$ 1,474,185
Total Loans	1,651,199	1,474,185
Non-Accrual Status	4,277	0
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	1,230	0
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due	4,277	0
Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Current	1,553,547	1,414,139
Total Loans	1,554,777	1,414,139
Non-Accrual Status	0	0
Commercial Mortgage Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Commercial Mortgage Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	1,230	0
Commercial Mortgage Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans
Financing Receivable, Past Due [Line Items]
Current	88,237	60,046
Total Loans	92,514	60,046
Non-Accrual Status	4,277	0
Agricultural Property Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due	4,277	0
Other collateralized loans
Financing Receivable, Past Due [Line Items]
Current	3,908
Total Loans	3,908
Non-Accrual Status	0
Other collateralized loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0
Other collateralized loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0
Other collateralized loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0
Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Accruing Interest	$ 0	$ 0