Investments Investments (Analysis of Past Due Commercial Mortgage, Agricultural and Other Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Current	$ 1,234,182	$ 438,815
Financing Receivable, Total Recorded Investment	1,234,182	438,815
Financing Receivable, Recorded Investment, Non-Accrual Status	0	0
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Greater than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Commercial mortgage and other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Current	1,149,947	386,149
Financing Receivable, Total Recorded Investment	1,149,947	386,149
Financing Receivable, Recorded Investment, Non-Accrual Status	0	0
Commercial mortgage and other loans | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Commercial mortgage and other loans | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Commercial mortgage and other loans | Financing Receivables, Greater than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Agricultural Property Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Current	84,235	49,926
Financing Receivable, Total Recorded Investment	84,235	49,926
Financing Receivable, Recorded Investment, Non-Accrual Status	0	0
Agricultural Property Loans | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Agricultural Property Loans | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Agricultural Property Loans | Financing Receivables, Greater than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Uncollateralized loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Current	0	2,740
Financing Receivable, Total Recorded Investment	0	2,740
Financing Receivable, Recorded Investment, Non-Accrual Status	0	0
Uncollateralized loans | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Uncollateralized loans | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Uncollateralized loans | Financing Receivables, Greater than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 0	$ 0