Investments (Credit Quality Indicators) (Details) - Commercial Mortgage and Agricultural Loans - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Greater than 1.2X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	$ 981,593	$ 997,610
Greater than 1.2X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	416,953	372,958
Greater than 1.2X | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	209,576	177,956
Greater than 1.2X | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	0	2,991
Greater than 1.2X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	1,608,122	1,551,515
1.0X to 1.2X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	16,345	24,491
1.0X to 1.2X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	25,060	15,741
1.0X to 1.2X | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	10,715	31,463
1.0X to 1.2X | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	18,826	22,068
1.0X to 1.2X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	70,946	93,763
Less than 1.0X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	16,715	9,393
Less than 1.0X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	4,057	13,981
Less than 1.0X | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	0	3,493
Less than 1.0X | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	5,026	5,152
Less than 1.0X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	25,798	32,019
Total | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	1,014,653	1,031,494
Total | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	446,070	402,680
Total | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	220,291	212,912
Total | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	23,852	30,211
Total | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	$ 1,704,866	$ 1,677,297