Investments (Credit Quality Indicators) (Details) - Commercial Mortgage and Agricultural Loans - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Greater than 1.2X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	$ 1,007,922	$ 997,610
Greater than 1.2X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	412,585	372,958
Greater than 1.2X | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	214,071	177,956
Greater than 1.2X | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	2,965	2,991
Greater than 1.2X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	1,637,543	1,551,515
1.0X to 1.2X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	16,437	24,491
1.0X to 1.2X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	28,865	15,741
1.0X to 1.2X | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	18,096	31,463
1.0X to 1.2X | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	15,875	22,068
1.0X to 1.2X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	79,273	93,763
Less than 1.0X | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	16,637	9,393
Less than 1.0X | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	4,097	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	5,068	5,152
Less than 1.0X | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	25,802	32,019
Total | 0%-59.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	1,040,996	1,031,494
Total | 60%-69.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	445,547	402,680
Total | 70%-79.99%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	232,167	212,912
Total | Greater than 80%
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	23,908	30,211
Total | Total
Credit Quality Indicators [Line Items]
Total commercial mortgage and agricultural property loans	$ 1,742,618	$ 1,677,297