Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 6,160,410	$ 4,948,943
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,142,205	777,192
One Year Prior	782,796	1,248,477
Two Year Prior	1,261,597	354,746
Three Year Prior	363,599	511,628
Four Year Prior	528,288	265,253
Prior	1,514,519	1,324,629
Recording investment gross of allowance for credit losses	5,593,004	4,481,925
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,038,315	744,301
One Year Prior	779,282	1,248,477
Two Year Prior	1,261,597	243,325
Three Year Prior	292,561	452,626
Four Year Prior	497,407	258,617
Prior	1,402,831	1,203,807
Recording investment gross of allowance for credit losses	5,271,993	4,151,153
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	103,890	32,891
One Year Prior	3,514	0
Two Year Prior	0	83,655
Three Year Prior	0	26,558
Four Year Prior	15,632	6,636
Prior	40,521	45,742
Recording investment gross of allowance for credit losses	163,557	195,482
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	27,766
Three Year Prior	71,038	32,444
Four Year Prior	15,249	0
Prior	71,167	75,080
Recording investment gross of allowance for credit losses	157,454	135,290
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	126,949	264,918
One Year Prior	235,585	133,126
Two Year Prior	132,042	25,894
Three Year Prior	25,875	16,053
Four Year Prior	15,824	6,327
Prior	25,771	20,700
Recording investment gross of allowance for credit losses	562,046	467,018
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	126,949	262,918
One Year Prior	233,585	133,126
Two Year Prior	130,353	25,894
Three Year Prior	24,063	16,053
Four Year Prior	15,824	6,327
Prior	25,771	20,700
Recording investment gross of allowance for credit losses	556,545	465,018
Agricultural Property Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	2,000
One Year Prior	2,000	0
Two Year Prior	0	0
Three Year Prior	1,812	0
Four Year Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	3,812	2,000
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	1,689	0
Three Year Prior	0	0
Four Year Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	1,689	0
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	249,037	266,453
One Year Prior	245,914	262,095
Two Year Prior	482,718	63,558
Three Year Prior	109,249	222,638
Four Year Prior	265,053	201,087
Prior	1,068,763	894,646
Recording investment gross of allowance for credit losses	2,420,734	1,910,477
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	73,774	208,708
One Year Prior	179,375	133,126
Two Year Prior	132,042	25,894
Three Year Prior	25,875	16,053
Four Year Prior	15,824	6,327
Prior	25,771	20,700
Recording investment gross of allowance for credit losses	452,661	410,808
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	675,153	344,110
One Year Prior	355,984	681,996
Two Year Prior	449,878	243,800
Three Year Prior	172,721	219,593
Four Year Prior	225,803	61,757
Prior	206,237	305,175
Recording investment gross of allowance for credit losses	2,085,776	1,856,431
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	47,489	56,210
One Year Prior	56,210	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	103,699	56,210
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	218,015	166,629
One Year Prior	133,343	304,386
Two Year Prior	255,299	47,388
Three Year Prior	77,812	66,148
Four Year Prior	20,924	2,409
Prior	86,806	53,336
Recording investment gross of allowance for credit losses	792,199	640,296
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	5,686	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	5,686	0
80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Year Prior	47,555	0
Two Year Prior	73,702	0
Three Year Prior	3,817	3,249
Four Year Prior	16,508	0
Prior	152,713	71,472
Recording investment gross of allowance for credit losses	294,295	74,721
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