Investments (Allowance for Credit Losses and Recorded Investment in Commercial Mortgage and Other Loans) (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Allowance for Credit Losses:
Individually evaluated for impairment	$ (761,000)	$ (940,000)
Collectively evaluated for impairment	3,038,000	3,214,000
Total ending balance	3,799,000	4,154,000
Recorded Investment:
Gross of reserves: individually evaluated for impairment	22,654,000	15,875,000
Gross of reserves: collectively evaluated for impairment	1,690,622,000	1,669,832,000
Total ending balance, gross of reserves	1,713,276,000	1,685,707,000
Impaired Financing Receivable, Recorded Investment	15,900,000	15,900,000
Agricultural loans
Allowance for Credit Losses:
Collectively evaluated for impairment	100,000	100,000
Uncollateralized loans
Recorded Investment:
Gross of reserves: individually evaluated for impairment	0	0
Gross of reserves: collectively evaluated for impairment	8,000,000	8,000,000
Agricultural Loan | Class Of Financing Receivable
Recorded Investment:
Gross of reserves: individually evaluated for impairment	300,000	0
Impaired Financing Receivable, Recorded Investment	$ 111,000,000	$ 115,000,000