Investments (Loan-to-value ratios) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 24,491
2019	168,637
2018	197,241
2017	176,916
2016	263,879
Prior	350,148
Revolving Loans	0
Recording investment gross of allowance for credit losses	1,181,312
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	6,486
2016	0
Prior	14,393
Revolving Loans	0
Recording investment gross of allowance for credit losses	20,879
Commercial Mortgage and Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	24,491
2019	168,637
2018	197,241
2017	183,402
2016	263,879
Prior	364,541
Revolving Loans	0
Recording investment gross of allowance for credit losses	1,202,191
0%-59.99% \| Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	57,680
2018	35,787
2017	90,979
2016	164,124
Prior	256,759
Revolving Loans	0
Recording investment gross of allowance for credit losses	605,329
0%-59.99% \| Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	6,486
2016	0
Prior	14,393
Revolving Loans	0
Recording investment gross of allowance for credit losses	20,879
0%-59.99% \| Commercial Mortgage and Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	57,680
2018	35,787
2017	97,465
2016	164,124
Prior	271,152
Revolving Loans	0
Recording investment gross of allowance for credit losses	626,208
60%-69.99% \| Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	16,864
2019	65,000
2018	80,324
2017	53,111
2016	90,127
Prior	91,606
Revolving Loans	0
Recording investment gross of allowance for credit losses	397,032
60%-69.99% \| Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	0
60%-69.99% \| Commercial Mortgage and Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	16,864
2019	65,000
2018	80,324
2017	53,111
2016	90,127
Prior	91,606
Revolving Loans	0
Recording investment gross of allowance for credit losses	397,032
70%-79.99% \| Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,627
2019	45,957
2018	81,130
2017	32,826
2016	9,628
Prior	1,561
Revolving Loans	0
Recording investment gross of allowance for credit losses	178,729
70%-79.99% \| Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	0
70%-79.99% \| Commercial Mortgage and Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,627
2019	45,957
2018	81,130
2017	32,826
2016	9,628
Prior	1,561
Revolving Loans	0
Recording investment gross of allowance for credit losses	178,729
80% or greater \| Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	222
Revolving Loans	0
Recording investment gross of allowance for credit losses	222
80% or greater \| Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	0
80% or greater \| Commercial Mortgage and Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	222
Revolving Loans	0
Recording investment gross of allowance for credit losses	222
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	1,181,312	$ 1,219,456
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 20,879	$ 22,197

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Amount, before allowance for credit loss, of financing receivable.

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