Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 5,519,969	$ 4,948,943
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	587,613	777,192
One Year Prior	779,524	1,248,477
Two Year Prior	1,254,160	354,746
Three Year Prior	353,580	511,628
Four Year Prior	507,014	265,253
Prior	1,523,160	1,324,629
Revolving Loans	0
Recording investment gross of allowance for credit losses	5,005,051	4,481,925
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	495,769	744,301
One Year Prior	775,990	1,248,477
Two Year Prior	1,254,160	243,325
Three Year Prior	282,245	452,626
Four Year Prior	468,051	258,617
Prior	1,422,566	1,203,807
Revolving Loans	0
Recording investment gross of allowance for credit losses	4,698,781	4,151,153
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	91,844	32,891
One Year Prior	3,534	0
Two Year Prior	0	83,655
Three Year Prior	0	26,558
Four Year Prior	23,667	6,636
Prior	7,904	45,742
Revolving Loans	0
Recording investment gross of allowance for credit losses	126,949	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	71,335	32,444
Four Year Prior	15,296	0
Prior	92,690	75,080
Revolving Loans	0
Recording investment gross of allowance for credit losses	179,321	135,290
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	67,185	264,918
One Year Prior	242,681	133,126
Two Year Prior	132,028	25,894
Three Year Prior	26,052	16,053
Four Year Prior	15,880	6,327
Prior	26,342	20,700
Revolving Loans	4,750
Recording investment gross of allowance for credit losses	514,918	467,018
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	67,185	262,918
One Year Prior	240,681	133,126
Two Year Prior	132,028	25,894
Three Year Prior	26,052	16,053
Four Year Prior	15,880	6,327
Prior	26,342	20,700
Revolving Loans	4,750
Recording investment gross of allowance for credit losses	512,918	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	0	0
Four Year Prior	0	0
Prior	0	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	2,000	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	0	0
Three Year Prior	0	0
Four Year Prior	0	0
Prior	0	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	0	0
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	195,586	266,453
One Year Prior	245,400	262,095
Two Year Prior	454,857	63,558
Three Year Prior	98,187	222,638
Four Year Prior	256,820	201,087
Prior	1,126,765	894,646
Revolving Loans	0
Recording investment gross of allowance for credit losses	2,377,615	1,910,477
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	27,184	208,708
One Year Prior	186,471	133,126
Two Year Prior	132,028	25,894
Three Year Prior	26,052	16,053
Four Year Prior	15,880	6,327
Prior	26,342	20,700
Revolving Loans	4,750
Recording investment gross of allowance for credit losses	418,707	410,808
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	194,755	344,110
One Year Prior	378,576	681,996
Two Year Prior	503,195	243,800
Three Year Prior	180,257	219,593
Four Year Prior	215,928	61,757
Prior	188,358	305,175
Revolving Loans	0
Recording investment gross of allowance for credit losses	1,661,069	1,856,431
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	34,315	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
Revolving Loans	0
Recording investment gross of allowance for credit losses	90,525	56,210
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	197,272	166,629
One Year Prior	155,548	304,386
Two Year Prior	222,693	47,388
Three Year Prior	71,335	66,148
Four Year Prior	20,950	2,409
Prior	74,022	53,336
Revolving Loans	0
Recording investment gross of allowance for credit losses	741,820	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
Revolving Loans	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	0	0
Two Year Prior	73,415	0
Three Year Prior	3,801	3,249
Four Year Prior	13,316	0
Prior	134,015	71,472
Revolving Loans	0
Recording investment gross of allowance for credit losses	224,547	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
Revolving Loans	0
Recording investment gross of allowance for credit losses	$ 0	$ 0