Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 7,267,877	$ 6,160,410
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,168,980	1,142,205
One Year Prior	1,145,722	782,796
Two Year Prior	782,305	1,261,597
Three Year Prior	1,266,256	363,599
Four Year Prior	330,836	528,288
Prior	1,860,460	1,514,519
Revolving Loans	2,554
Recording investment gross of allowance for credit losses	6,557,113	5,593,004
Commercial mortgage loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,119,178	1,038,315
One Year Prior	1,041,778	779,282
Two Year Prior	767,191	1,261,597
Three Year Prior	1,266,256	292,561
Four Year Prior	260,688	497,407
Prior	1,740,855	1,402,831
Revolving Loans	2,554
Recording investment gross of allowance for credit losses	6,198,500	5,271,993
Commercial mortgage loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	49,802	103,890
One Year Prior	103,944	3,514
Two Year Prior	15,114	0
Three Year Prior	0	0
Four Year Prior	0	15,632
Prior	57,284	40,521
Revolving Loans	0
Recording investment gross of allowance for credit losses	226,144	163,557
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	71,038
Four Year Prior	70,148	15,249
Prior	62,321	71,167
Revolving Loans	0
Recording investment gross of allowance for credit losses	132,469	157,454
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	137,525	126,949
One Year Prior	109,823	235,585
Two Year Prior	224,868	132,042
Three Year Prior	131,740	25,875
Four Year Prior	25,321	15,824
Prior	39,716	25,771
Revolving Loans	34,316
Recording investment gross of allowance for credit losses	703,309	562,046
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	134,137	126,949
One Year Prior	95,734	233,585
Two Year Prior	215,626	130,353
Three Year Prior	130,030	24,063
Four Year Prior	23,625	15,824
Prior	39,716	25,771
Revolving Loans	18,988
Recording investment gross of allowance for credit losses	657,856	556,545
Agricultural Property Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	3,388	0
One Year Prior	14,089	2,000
Two Year Prior	9,242	0
Three Year Prior	0	1,812
Four Year Prior	1,696	0
Prior	0	0
Revolving Loans	15,328
Recording investment gross of allowance for credit losses	43,743	3,812
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	1,689
Three Year Prior	1,710	0
Four Year Prior	0	0
Prior	0	0
Revolving Loans	0
Recording investment gross of allowance for credit losses	1,710	1,689
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	123,866	249,037
One Year Prior	251,014	245,914
Two Year Prior	272,694	482,718
Three Year Prior	484,606	109,249
Four Year Prior	76,205	265,053
Prior	1,219,508	1,068,763
Revolving Loans	2,554
Recording investment gross of allowance for credit losses	2,430,447	2,420,734
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	137,525	73,774
One Year Prior	90,427	179,375
Two Year Prior	168,416	132,042
Three Year Prior	131,740	25,875
Four Year Prior	23,625	15,824
Prior	39,716	25,771
Revolving Loans	18,988
Recording investment gross of allowance for credit losses	610,437	452,661
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	873,753	675,153
One Year Prior	692,435	355,984
Two Year Prior	298,812	449,878
Three Year Prior	401,981	172,721
Four Year Prior	173,843	225,803
Prior	358,886	206,237
Revolving Loans	0
Recording investment gross of allowance for credit losses	2,799,710	2,085,776
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	47,489
One Year Prior	19,396	56,210
Two Year Prior	49,210	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	68,606	103,699
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	170,165	218,015
One Year Prior	202,273	133,343
Two Year Prior	151,128	255,299
Three Year Prior	295,221	77,812
Four Year Prior	76,922	20,924
Prior	50,697	86,806
Revolving Loans	0
Recording investment gross of allowance for credit losses	946,406	792,199
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	5,686
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	5,686
80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	1,196	0
One Year Prior	0	47,555
Two Year Prior	59,671	73,702
Three Year Prior	84,448	3,817
Four Year Prior	3,866	16,508
Prior	231,369	152,713
Revolving Loans	0
Recording investment gross of allowance for credit losses	380,550	294,295
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	7,242	0
Three Year Prior	0	0
Four Year Prior	1,696	0
Prior	0	0
Revolving Loans	15,328
Recording investment gross of allowance for credit losses	$ 24,266	$ 0