Investments (Credit Quality Indicators) (Details) (Commercial Mortgage and Agricultural Loans [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Debt Service Coverage Ratio, Greater than One Point Two X [Member] | Loan To Value Ratio Less Than Fifty Nine Point Nine Nine Percent [Member]
Financing Receivable	$ 1,010,032	$ 997,610
Debt Service Coverage Ratio, Greater than One Point Two X [Member] | Loan-to-Value Ratio, Sixty Percent To Sixty Nine Point Nine Nine Percent [Member]
Financing Receivable	404,088	372,958
Debt Service Coverage Ratio, Greater than One Point Two X [Member] | Loan-to-Value Ratio, Seventy Percent To Seventy Nine Point Nine Nine Percent [Member]
Financing Receivable	198,461	177,956
Debt Service Coverage Ratio, Greater than One Point Two X [Member] | Loan To Value Ratio, Greater Than Eighty Percent [Member]
Financing Receivable	3,323	2,991
Debt Service Coverage Ratio, Greater than One Point Two X [Member] | Loan To Value Ratio Total [Member]
Financing Receivable	1,615,904	1,551,515
Debt Service Coverage Ratio, One Point Zero X to Less Than One Point Two X [Member] | Loan To Value Ratio Less Than Fifty Nine Point Nine Nine Percent [Member]
Financing Receivable	14,958	24,491
Debt Service Coverage Ratio, One Point Zero X to Less Than One Point Two X [Member] | Loan-to-Value Ratio, Sixty Percent To Sixty Nine Point Nine Nine Percent [Member]
Financing Receivable	9,764	15,741
Debt Service Coverage Ratio, One Point Zero X to Less Than One Point Two X [Member] | Loan-to-Value Ratio, Seventy Percent To Seventy Nine Point Nine Nine Percent [Member]
Financing Receivable	18,230	31,463
Debt Service Coverage Ratio, One Point Zero X to Less Than One Point Two X [Member] | Loan To Value Ratio, Greater Than Eighty Percent [Member]
Financing Receivable	22,016	22,068
Debt Service Coverage Ratio, One Point Zero X to Less Than One Point Two X [Member] | Loan To Value Ratio Total [Member]
Financing Receivable	64,968	93,763
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan To Value Ratio Less Than Fifty Nine Point Nine Nine Percent [Member]
Financing Receivable	15,757	9,393
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan-to-Value Ratio, Sixty Percent To Sixty Nine Point Nine Nine Percent [Member]
Financing Receivable	19,704	13,981
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan-to-Value Ratio, Seventy Percent To Seventy Nine Point Nine Nine Percent [Member]
Financing Receivable	0	3,493
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan To Value Ratio, Greater Than Eighty Percent [Member]
Financing Receivable	5,842	5,152
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan To Value Ratio Total [Member]
Financing Receivable	41,303	32,019
Debt Service Coverage Ratio Total [Member] | Loan To Value Ratio Less Than Fifty Nine Point Nine Nine Percent [Member]
Financing Receivable	1,040,747	1,031,494
Debt Service Coverage Ratio Total [Member] | Loan-to-Value Ratio, Sixty Percent To Sixty Nine Point Nine Nine Percent [Member]
Financing Receivable	433,556	402,680
Debt Service Coverage Ratio Total [Member] | Loan-to-Value Ratio, Seventy Percent To Seventy Nine Point Nine Nine Percent [Member]
Financing Receivable	216,691	212,912
Debt Service Coverage Ratio Total [Member] | Loan To Value Ratio, Greater Than Eighty Percent [Member]
Financing Receivable	31,181	30,211
Debt Service Coverage Ratio Total [Member] | Loan To Value Ratio Total [Member]
Financing Receivable	$ 1,722,175	$ 1,677,297