Investments (Credit Quality Indicators) (Details) - Commercial Mortgage and Agricultural Loans - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	$ 1,277,362	$ 1,234,182
1.2X or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	1,240,884	1,192,274
1.0X to 1.2X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	35,928	32,414
Less than 1.0X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	550	9,494
0%-59.99%
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	695,619	688,582
0%-59.99% | 1.2X or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	679,334	667,051
0%-59.99% | 1.0X to 1.2X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	15,735	16,921
0%-59.99% | Less than 1.0X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	550	4,610
60%-69.99%
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	453,752	410,545
60%-69.99% | 1.2X or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	449,992	406,728
60%-69.99% | 1.0X to 1.2X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	3,760	0
60%-69.99% | Less than 1.0X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	0	3,817
70%-79.99%
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	117,204	124,263
70%-79.99% | 1.2X or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	101,832	108,770
70%-79.99% | 1.0X to 1.2X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	15,372	15,493
70%-79.99% | Less than 1.0X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	0	0
80% or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	10,787	10,792
80% or greater | 1.2X or greater
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	9,726	9,725
80% or greater | 1.0X to 1.2X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	1,061	0
80% or greater | Less than 1.0X
Credit Quality Indicators [Line Items]
Financing Receivable, Gross	$ 0	$ 1,067