Investments (Allowance for Credit Losses and Recorded Investment in Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Allowance for Credit Losses:
Individually evaluated for impairment	$ (761)	$ (940)
Collectively evaluated for impairment	3,114	3,214
Total ending balance	3,875	4,154
Recorded Investment:
Gross of reserves: individually evaluated for impairment	22,672	15,875
Gross of reserves: collectively evaluated for impairment	1,728,356	1,669,832
Total ending balance, gross of reserves	1,751,028	1,685,707
Impaired Financing Receivable, Recorded Investment	22,700	15,900
Agricultural Property Loans
Allowance for Credit Losses:
Collectively evaluated for impairment	100	100
Uncollateralized loans
Recorded Investment:
Gross of reserves: collectively evaluated for impairment	8,000	8,000
Agricultural Loan | Class Of Financing Receivable
Recorded Investment:
Impaired Financing Receivable, Recorded Investment	$ 112,000	$ 115,000