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	$ 2,983,584	$ 2,838,511
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	173,065	518,611
One Year Prior	517,793	311,413
Two Year Prior	311,275	544,189
Three Year Prior	540,844	260,828
Four Year Prior	260,066	309,083
Prior	987,029	722,051
Recording investment gross of allowance for credit losses	2,790,072	2,666,175
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	173,065	501,456
One Year Prior	500,852	195,164
Two Year Prior	195,538	481,289
Three Year Prior	478,368	253,938
Four Year Prior	253,238	289,443
Prior	884,585	638,092
Recording investment gross of allowance for credit losses	2,485,646	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	16,941	109,862
Two Year Prior	109,430	39,577
Three Year Prior	39,338	6,890
Four Year Prior	6,828	7,100
Prior	45,716	39,213
Recording investment gross of allowance for credit losses	218,253	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	6,307	23,323
Three Year Prior	23,138	0
Four Year Prior	0	12,540
Prior	56,728	44,746
Recording investment gross of allowance for credit losses	86,173	86,996
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	25,000	98,579
One Year Prior	98,527	26,581
Two Year Prior	26,363	16,226
Three Year Prior	16,181	6,463
Four Year Prior	6,452	8,372
Prior	20,989	16,115
Recording investment gross of allowance for credit losses	193,512	172,336
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	25,000	98,579
One Year Prior	98,527	26,581
Two Year Prior	26,363	16,226
Three Year Prior	16,181	6,463
Four Year Prior	6,452	8,372
Prior	20,174	15,300
Recording investment gross of allowance for credit losses	192,697	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	815	815
Recording investment gross of allowance for credit losses	815	815
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	47,161
One Year Prior	47,159	0
Two Year Prior	0	179,682
Three Year Prior	177,478	76,656
Four Year Prior	75,987	126,934
Prior	643,413	553,022
Recording investment gross of allowance for credit losses	944,037	983,455
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	25,000	98,579
One Year Prior	98,527	26,581
Two Year Prior	26,363	16,226
Three Year Prior	16,181	6,463
Four Year Prior	6,452	8,372
Prior	20,989	16,115
Recording investment gross of allowance for credit losses	193,512	172,336
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	40,360	307,999
One Year Prior	307,625	225,330
Two Year Prior	235,943	289,322
Three Year Prior	290,954	170,444
Four Year Prior	170,351	126,159
Prior	261,320	116,654
Recording investment gross of allowance for credit losses	1,306,553	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	132,705	163,451
One Year Prior	163,009	86,083
Two Year Prior	75,332	75,185
Three Year Prior	72,412	13,728
Four Year Prior	13,728	55,032
Prior	81,343	51,203
Recording investment gross of allowance for credit losses	538,529	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	953	1,172
Recording investment gross of allowance for credit losses	953	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