Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 1,480,298	$ 1,508,259
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	856,751
One Year Prior	838,147	81,058
Two Years Prior	81,058	48,043
Three Years Prior	47,927	17,698
Four Years Prior	17,656	153,063
Prior	445,629	301,346
Recording investment gross of allowance for credit losses	1,430,417	1,457,959
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	856,751
One Year Prior	838,147	81,058
Two Years Prior	81,058	48,043
Three Years Prior	47,927	7,140
Four Years Prior	7,140	119,807
Prior	406,501	295,148
Recording investment gross of allowance for credit losses	1,380,773	1,407,947
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	10,558
Four Years Prior	10,516	0
Prior	0	0
Recording investment gross of allowance for credit losses	10,516	10,558
Commercial mortgage loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	33,256
Prior	39,128	6,198
Recording investment gross of allowance for credit losses	39,128	39,454
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	39,958
One Year Prior	39,720	840
Two Years Prior	829	0
Three Years Prior	0	0
Four Years Prior	0	2,695
Prior	9,332	6,807
Recording investment gross of allowance for credit losses	49,881	50,300
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	39,958
One Year Prior	39,720	840
Two Years Prior	829	0
Three Years Prior	0	0
Four Years Prior	0	2,695
Prior	5,893	3,368
Recording investment gross of allowance for credit losses	46,442	46,861
Agricultural Property Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	0	0
Agricultural Property Loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	3,439	3,439
Recording investment gross of allowance for credit losses	3,439	3,439
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	150,485
One Year Prior	150,485	0
Two Years Prior	0	20,966
Three Years Prior	20,906	7,140
Four Years Prior	7,140	92,932
Prior	316,588	232,249
Recording investment gross of allowance for credit losses	495,119	503,772
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	39,958
One Year Prior	39,720	840
Two Years Prior	829	0
Three Years Prior	0	0
Four Years Prior	0	2,695
Prior	9,332	6,807
Recording investment gross of allowance for credit losses	49,881	50,300
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	389,476
One Year Prior	377,424	32,920
Two Years Prior	32,920	9,870
Three Years Prior	9,854	10,558
Four Years Prior	10,516	39,001
Prior	66,569	27,621
Recording investment gross of allowance for credit losses	497,283	509,446
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	0	0
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	316,790
One Year Prior	310,238	48,138
Two Years Prior	48,138	17,207
Three Years Prior	17,167	0
Four Years Prior	0	21,130
Prior	42,125	21,121
Recording investment gross of allowance for credit losses	417,668	424,386
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	0	0
80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	20,347	20,355
Recording investment gross of allowance for credit losses	20,347	20,355
80% or greater | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	$ 0	$ 0