Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 8,094,203	$ 7,797,038
Total commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	286,127	1,788,998
One Year Prior	1,796,239	1,139,236
Two Year Prior	1,141,663	770,354
Three Year Prior	765,856	1,258,169
Four Year Prior	1,262,729	255,562
Prior	1,962,277	1,736,220
Revolving Loans	8,667	6,479
Recording investment gross of allowance for credit losses	7,223,558	6,955,018
Total commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	286,127	1,728,895
One Year Prior	1,736,155	962,290
Two Year Prior	963,036	755,350
Three Year Prior	750,965	1,256,699
Four Year Prior	1,261,264	255,562
Prior	1,843,067	1,616,904
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	6,840,614	6,575,700
Total commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	60,103
One Year Prior	60,084	176,946
Two Year Prior	178,627	15,004
Three Year Prior	14,891	0
Four Year Prior	0	0
Prior	55,934	59,871
Revolving Loans	8,667	6,479
Recording investment gross of allowance for credit losses	318,203	318,403
Total commercial mortgage 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	1,470
Four Year Prior	1,465	0
Prior	63,276	59,445
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	64,741	60,915
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	40,299	271,275
One Year Prior	270,935	108,965
Two Year Prior	94,408	220,325
Three Year Prior	218,650	131,581
Four Year Prior	131,519	25,145
Prior	62,320	38,478
Revolving Loans	40,005	34,272
Recording investment gross of allowance for credit losses	858,136	830,041
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	40,299	259,647
One Year Prior	259,307	95,087
Two Year Prior	92,050	211,030
Three Year Prior	206,492	129,865
Four Year Prior	124,641	23,488
Prior	48,428	38,478
Revolving Loans	24,338	18,834
Recording investment gross of allowance for credit losses	795,555	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	11,628	13,878
Two Year Prior	2,358	9,295
Three Year Prior	12,158	0
Four Year Prior	0	0
Prior	10,240	0
Revolving Loans	15,667	15,438
Recording investment gross of allowance for credit losses	52,051	50,239
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	1,716
Four Year Prior	6,878	1,657
Prior	3,652	0
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	10,530	3,373
0%-59.99% | Total commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	38,195	452,940
One Year Prior	457,963	232,276
Two Year Prior	333,678	306,684
Three Year Prior	306,930	482,596
Four Year Prior	481,026	134,403
Prior	1,295,238	1,138,394
Revolving Loans	8,667	6,479
Recording investment gross of allowance for credit losses	2,921,697	2,753,772
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	22,300	241,715
One Year Prior	241,375	89,569
Two Year Prior	75,069	163,820
Three Year Prior	162,037	126,368
Four Year Prior	126,284	23,488
Prior	60,701	38,478
Revolving Loans	24,338	18,834
Recording investment gross of allowance for credit losses	712,104	702,272
60%-69.99% | Total commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	247,932	972,161
One Year Prior	972,650	541,849
Two Year Prior	443,420	273,258
Three Year Prior	276,319	360,457
Four Year Prior	362,180	110,515
Prior	387,446	303,107
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	2,689,947	2,561,347
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	29,560
One Year Prior	29,560	19,396
Two Year Prior	19,339	49,210
Three Year Prior	49,210	0
Four Year Prior	0	0
Prior	1,619	0
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	99,728	98,166
70%-79.99% | Total commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	362,701
One Year Prior	364,430	365,111
Two Year Prior	364,565	134,208
Three Year Prior	170,981	330,355
Four Year Prior	334,446	6,774
Prior	81,122	77,399
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	1,315,544	1,276,548
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	17,999	0
One Year Prior	0	0
Two Year Prior	0	0
Three Year Prior	0	5,213
Four Year Prior	5,235	0
Prior	0	0
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	23,234	5,213
80% or greater | Total commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	1,196
One Year Prior	1,196	0
Two Year Prior	0	56,204
Three Year Prior	11,626	84,761
Four Year Prior	85,077	3,870
Prior	198,471	217,320
Revolving Loans	0	0
Recording investment gross of allowance for credit losses	296,370	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	7,403	0
Four Year Prior	0	1,657
Prior	0	0
Revolving Loans	15,667	15,438
Recording investment gross of allowance for credit losses	$ 23,070	$ 24,390