Investments (Analysis of Past Due Commercial Mortgage, Agricultural and Other Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 1,271,081	$ 1,356,374
Total Loans	1,271,081	1,356,374
Non-Accrual Status	0	0
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Commercial Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,217,673	1,301,999
Total Loans	1,217,673	1,301,999
Non-Accrual Status	0	0
Commercial Mortgage Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Commercial Mortgage Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Commercial Mortgage Loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	53,408	54,375
Total Loans	53,408	54,375
Non-Accrual Status	0	0
Agricultural Property Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Agricultural Property Loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Interest	$ 0	$ 0