Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 9,751,528	$ 7,797,038
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,630,649	1,788,998
One Year Prior	1,796,410	1,139,236
Two Year Prior	1,144,922	770,354
Three Year Prior	728,690	1,258,169
Four Year Prior	1,274,692	255,562
Prior	1,902,291	1,736,220
Revolving Loans	10,846	6,479
Recording investment gross of allowance for credit losses	8,488,500	6,955,018
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,576,432	1,728,895
One Year Prior	1,728,076	962,290
Two Year Prior	852,057	755,350
Three Year Prior	699,115	1,256,699
Four Year Prior	1,273,236	255,562
Prior	1,773,232	1,616,904
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	7,902,148	6,575,700
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	34,180	60,103
One Year Prior	60,019	176,946
Two Year Prior	292,865	15,004
Three Year Prior	11,296	0
Four Year Prior	0	0
Prior	68,611	59,871
Revolving Loans	10,846	6,479
Recording investment gross of allowance for credit losses	477,817	318,403
Commercial mortgage loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	20,037	0
One Year Prior	8,315	0
Two Year Prior	0	0
Three Year Prior	18,279	1,470
Four Year Prior	1,456	0
Prior	60,448	59,445
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	108,535	60,915
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	191,248	271,275
One Year Prior	272,221	108,965
Two Year Prior	94,030	220,325
Three Year Prior	216,980	131,581
Four Year Prior	131,381	25,145
Prior	61,640	38,478
Revolving Loans	53,039	34,272
Recording investment gross of allowance for credit losses	1,020,539	830,041
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	191,248	259,647
One Year Prior	260,619	95,087
Two Year Prior	91,672	211,030
Three Year Prior	159,049	129,865
Four Year Prior	124,621	23,488
Prior	47,965	38,478
Revolving Loans	40,414	18,834
Recording investment gross of allowance for credit losses	915,588	776,429
Agricultural Property Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	11,628
One Year Prior	10,640	13,878
Two Year Prior	2,358	9,295
Three Year Prior	4,755	0
Four Year Prior	0	0
Prior	10,261	0
Revolving Loans	0	15,438
Recording investment gross of allowance for credit losses	28,014	50,239
Agricultural Property Loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	962	0
Two Year Prior	0	0
Three Year Prior	53,176	1,716
Four Year Prior	6,760	1,657
Prior	3,414	0
Revolving Loans	12,625	0
Recording investment gross of allowance for credit losses	76,937	3,373
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	220,051
One Year Prior	11,457
Two Year Prior	141
Three Year Prior	0
Four Year Prior	0
Prior	0
Recording investment gross of allowance for credit losses	231,649
Residential mortgage loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	220,051
One Year Prior	11,457
Two Year Prior	141
Three Year Prior	0
Four Year Prior	0
Prior	0
Recording investment gross of allowance for credit losses	231,649
Residential mortgage loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0
One Year Prior	0
Two Year Prior	0
Three Year Prior	0
Four Year Prior	0
Prior	0
Recording investment gross of allowance for credit losses	0
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	469,939	452,940
One Year Prior	368,351	232,276
Two Year Prior	394,654	306,684
Three Year Prior	320,615	482,596
Four Year Prior	517,812	134,403
Prior	1,283,292	1,138,394
Revolving Loans	10,846	6,479
Recording investment gross of allowance for credit losses	3,365,509	2,753,772
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	179,447	241,715
One Year Prior	242,661	89,569
Two Year Prior	74,748	163,820
Three Year Prior	209,014	126,368
Four Year Prior	126,278	23,488
Prior	61,640	38,478
Revolving Loans	23,085	18,834
Recording investment gross of allowance for credit losses	916,873	702,272
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,067,364	972,161
One Year Prior	1,001,432	541,849
Two Year Prior	397,386	273,258
Three Year Prior	298,383	360,457
Four Year Prior	346,200	110,515
Prior	366,440	303,107
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	3,477,205	2,561,347
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	11,801	29,560
One Year Prior	29,560	19,396
Two Year Prior	19,282	49,210
Three Year Prior	2,000	0
Four Year Prior	0	0
Prior	0	0
Revolving Loans	17,329	0
Recording investment gross of allowance for credit losses	79,972	98,166
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	93,346	362,701
One Year Prior	385,078	365,111
Two Year Prior	352,882	134,208
Three Year Prior	73,066	330,355
Four Year Prior	281,626	6,774
Prior	29,027	77,399
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	1,215,025	1,276,548
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	5,213
Four Year Prior	5,103	0
Prior	0	0
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	5,103	5,213
80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	1,196
One Year Prior	41,549	0
Two Year Prior	0	56,204
Three Year Prior	36,626	84,761
Four Year Prior	129,054	3,870
Prior	223,532	217,320
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	430,761	363,351
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	7,295
Three Year Prior	5,966	0
Four Year Prior	0	1,657
Prior	0	0
Revolving Loans	12,625	15,438
Recording investment gross of allowance for credit losses	$ 18,591	$ 24,390