Investments (Credit Quality Indicators) (Details) - Commercial and agricultural mortgage loans - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 1,474,185	$ 1,356,374
0%-59.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	725,904	724,501
60% to 69.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	513,571	465,568
70%-79.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	233,713	163,285
80% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	997	3,020
≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	1,418,305	1,309,699
≥ 1.2X | 0%-59.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	715,654	709,342
≥ 1.2X | 60% to 69.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	499,493	442,308
≥ 1.2X | 70%-79.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	203,158	156,049
≥ 1.2X | 80% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	2,000
1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	52,271	46,330
1.0X to 1.2X | 0%-59.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	6,641	14,814
1.0X to 1.2X | 60% to 69.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	14,078	23,260
1.0X to 1.2X | 70%-79.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	30,555	7,236
1.0X to 1.2X | 80% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	997	1,020
Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,609	345
Less than 1.0X | 0%-59.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,609	345
Less than 1.0X | 60% to 69.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 70%-79.99%
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 80% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 0	$ 0