Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 3,076,855	$ 2,838,511
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	342,795	518,611
One Year Prior	518,254	311,413
Two Year Prior	314,437	544,189
Three Year Prior	510,185	260,828
Four Year Prior	252,192	309,083
Prior	945,309	722,051
Recording investment gross of allowance for credit losses	2,883,172	2,666,175
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	342,795	501,456
One Year Prior	501,528	195,164
Two Year Prior	199,237	481,289
Three Year Prior	448,221	253,938
Four Year Prior	245,427	289,443
Prior	843,926	638,092
Recording investment gross of allowance for credit losses	2,581,134	2,359,382
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	17,155
One Year Prior	16,726	109,862
Two Year Prior	108,998	39,577
Three Year Prior	39,097	6,890
Four Year Prior	6,765	7,100
Prior	45,452	39,213
Recording investment gross of allowance for credit losses	217,038	219,797
Commercial mortgage loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	6,387
Two Year Prior	6,202	23,323
Three Year Prior	22,867	0
Four Year Prior	0	12,540
Prior	55,931	44,746
Recording investment gross of allowance for credit losses	85,000	86,996
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	27,995	98,579
One Year Prior	99,101	26,581
Two Year Prior	26,184	16,226
Three Year Prior	16,121	6,463
Four Year Prior	6,343	8,372
Prior	17,939	16,115
Recording investment gross of allowance for credit losses	193,683	172,336
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	27,995	98,579
One Year Prior	99,101	26,581
Two Year Prior	26,184	16,226
Three Year Prior	16,121	6,463
Four Year Prior	6,343	8,372
Prior	17,151	15,300
Recording investment gross of allowance for credit losses	192,895	171,521
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 Year Prior	0	0
Three Year Prior	0	0
Four Year 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 Year Prior	0	0
Three Year Prior	0	0
Four Year Prior	0	0
Prior	788	815
Recording investment gross of allowance for credit losses	788	815
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	36,935	47,161
One Year Prior	47,157	0
Two Year Prior	5,584	179,682
Three Year Prior	164,712	76,656
Four Year Prior	83,681	126,934
Prior	619,216	553,022
Recording investment gross of allowance for credit losses	957,285	983,455
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	27,995	98,579
One Year Prior	99,101	26,581
Two Year Prior	26,184	16,226
Three Year Prior	16,121	6,463
Four Year Prior	6,343	8,372
Prior	17,939	16,115
Recording investment gross of allowance for credit losses	193,683	172,336
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	176,681	307,999
One Year Prior	324,556	225,330
Two Year Prior	237,578	289,322
Three Year Prior	273,374	170,444
Four Year Prior	165,783	126,159
Prior	250,876	116,654
Recording investment gross of allowance for credit losses	1,428,848	1,235,908
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Year Prior	0	0
Three Year Prior	0	0
Four Year 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	129,179	163,451
One Year Prior	146,541	86,083
Two Year Prior	71,275	75,185
Three Year Prior	72,099	13,728
Four Year Prior	2,728	55,032
Prior	74,270	51,203
Recording investment gross of allowance for credit losses	496,092	444,682
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Year Prior	0	0
Three Year Prior	0	0
Four Year 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 Year Prior	0	0
Three Year Prior	0	0
Four Year Prior	0	958
Prior	947	1,172
Recording investment gross of allowance for credit losses	947	2,130
80% or greater | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	0	0
Two Year Prior	0	0
Three Year Prior	0	0
Four Year Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	$ 0	$ 0