Summary of Investments - Fixed Maturities Unrealized Loss (Details) $ in Thousands	Sep. 30, 2024 USD ($) issue	Dec. 31, 2023 USD ($) issue
Number of Issues
Less than 12 months | issue	48	137
12 months or longer | issue	419	459
Fair Value
Less than 12 months	$ 137,701	$ 285,342
12 months or longer	858,775	960,788
Total	996,476	1,246,130
Gross Unrealized Loss
Less than 12 months	479	1,608
12 months or longer	66,334	89,740
Total	$ 66,813	$ 91,348
U.S. Treasury
Number of Issues
Less than 12 months | issue	0	2
12 months or longer | issue	7	6
Fair Value
Less than 12 months	$ 0	$ 4,138
12 months or longer	14,984	12,717
Total	14,984	16,855
Gross Unrealized Loss
Less than 12 months	0	46
12 months or longer	285	629
Total	$ 285	$ 675
U.S. government agency
Number of Issues
Less than 12 months | issue	0	3
12 months or longer | issue	23	23
Fair Value
Less than 12 months	$ 0	$ 10,986
12 months or longer	73,449	71,375
Total	73,449	82,361
Gross Unrealized Loss
Less than 12 months	0	14
12 months or longer	6,051	8,288
Total	$ 6,051	$ 8,302
General obligations | Midwest
Number of Issues
Less than 12 months | issue	2	11
12 months or longer | issue	2	3
Fair Value
Less than 12 months	$ 2,658	$ 19,534
12 months or longer	3,117	10,737
Total	5,775	30,271
Gross Unrealized Loss
Less than 12 months	2	61
12 months or longer	22	76
Total	$ 24	$ 137
General obligations | Northeast
Number of Issues
Less than 12 months | issue	0	3
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 0	$ 5,371
12 months or longer	3,463	3,469
Total	3,463	8,840
Gross Unrealized Loss
Less than 12 months	0	8
12 months or longer	20	35
Total	$ 20	$ 43
General obligations | South
Number of Issues
Less than 12 months | issue	0	12
12 months or longer | issue	11	9
Fair Value
Less than 12 months	$ 0	$ 21,753
12 months or longer	18,380	16,610
Total	18,380	38,363
Gross Unrealized Loss
Less than 12 months	0	91
12 months or longer	303	309
Total	$ 303	$ 400
General obligations | West
Number of Issues
Less than 12 months | issue	2	17
12 months or longer | issue	8	7
Fair Value
Less than 12 months	$ 3,313	$ 38,204
12 months or longer	22,357	20,064
Total	25,670	58,268
Gross Unrealized Loss
Less than 12 months	1	140
12 months or longer	230	331
Total	$ 231	$ 471
Special revenue | Midwest
Number of Issues
Less than 12 months | issue	5	17
12 months or longer | issue	11	11
Fair Value
Less than 12 months	$ 10,957	$ 29,535
12 months or longer	21,577	23,375
Total	32,534	52,910
Gross Unrealized Loss
Less than 12 months	33	113
12 months or longer	97	245
Total	$ 130	$ 358
Special revenue | Northeast
Number of Issues
Less than 12 months | issue	3	6
12 months or longer | issue	6	8
Fair Value
Less than 12 months	$ 4,969	$ 15,131
12 months or longer	18,743	24,271
Total	23,712	39,402
Gross Unrealized Loss
Less than 12 months	11	67
12 months or longer	249	493
Total	$ 260	$ 560
Special revenue | South
Number of Issues
Less than 12 months | issue	3	21
12 months or longer | issue	31	32
Fair Value
Less than 12 months	$ 6,441	$ 45,639
12 months or longer	70,370	66,925
Total	76,811	112,564
Gross Unrealized Loss
Less than 12 months	22	232
12 months or longer	1,258	1,923
Total	$ 1,280	$ 2,155
Special revenue | West
Number of Issues
Less than 12 months | issue	2	20
12 months or longer | issue	15	16
Fair Value
Less than 12 months	$ 2,254	$ 32,789
12 months or longer	36,856	38,495
Total	39,110	71,284
Gross Unrealized Loss
Less than 12 months	9	248
12 months or longer	443	588
Total	$ 452	$ 836
Foreign bonds
Number of Issues
Less than 12 months | issue	2	0
12 months or longer | issue	4	9
Fair Value
Less than 12 months	$ 10,170	$ 0
12 months or longer	9,236	19,172
Total	19,406	19,172
Gross Unrealized Loss
Less than 12 months	62	0
12 months or longer	658	2,083
Total	$ 720	$ 2,083
Public utilities
Number of Issues
Less than 12 months | issue	0	4
12 months or longer | issue	44	48
Fair Value
Less than 12 months	$ 0	$ 7,151
12 months or longer	100,064	111,793
Total	100,064	118,944
Gross Unrealized Loss
Less than 12 months	0	74
12 months or longer	6,513	9,980
Total	$ 6,513	$ 10,054
Corporate bonds | Energy
Number of Issues
Less than 12 months | issue	2	0
12 months or longer | issue	12	15
Fair Value
Less than 12 months	$ 1,520	$ 0
12 months or longer	30,557	34,331
Total	32,077	34,331
Gross Unrealized Loss
Less than 12 months	9	0
12 months or longer	1,395	2,127
Total	$ 1,404	$ 2,127
Corporate bonds | Industrials
Number of Issues
Less than 12 months | issue	1	1
12 months or longer | issue	18	21
Fair Value
Less than 12 months	$ 2,523	$ 1,210
12 months or longer	40,991	47,462
Total	43,514	48,672
Gross Unrealized Loss
Less than 12 months	22	19
12 months or longer	3,395	4,920
Total	$ 3,417	$ 4,939
Corporate bonds | Consumer goods and services
Number of Issues
Less than 12 months | issue	1	4
12 months or longer | issue	25	28
Fair Value
Less than 12 months	$ 933	$ 14,724
12 months or longer	64,510	68,837
Total	65,443	83,561
Gross Unrealized Loss
Less than 12 months	5	98
12 months or longer	5,720	7,567
Total	$ 5,725	$ 7,665
Corporate bonds | Health care
Number of Issues
Less than 12 months | issue	2	1
12 months or longer | issue	9	11
Fair Value
Less than 12 months	$ 5,236	$ 3,000
12 months or longer	22,563	26,544
Total	27,799	29,544
Gross Unrealized Loss
Less than 12 months	29	2
12 months or longer	3,707	4,497
Total	$ 3,736	$ 4,499
Corporate bonds | Technology, media and telecommunications
Number of Issues
Less than 12 months | issue	1	1
12 months or longer | issue	26	27
Fair Value
Less than 12 months	$ 994	$ 3,969
12 months or longer	61,896	62,988
Total	62,890	66,957
Gross Unrealized Loss
Less than 12 months	5	35
12 months or longer	4,699	5,630
Total	$ 4,704	$ 5,665
Corporate bonds | Financial services
Number of Issues
Less than 12 months | issue	1	5
12 months or longer | issue	29	44
Fair Value
Less than 12 months	$ 1,988	$ 14,327
12 months or longer	77,715	112,517
Total	79,703	126,844
Gross Unrealized Loss
Less than 12 months	8	223
12 months or longer	2,801	7,158
Total	$ 2,809	$ 7,381
Mortgage-backed securities
Number of Issues
Less than 12 months | issue	11	3
12 months or longer | issue	49	48
Fair Value
Less than 12 months	$ 60,221	$ 2,783
12 months or longer	17,234	15,758
Total	77,455	18,541
Gross Unrealized Loss
Less than 12 months	140	33
12 months or longer	1,779	2,295
Total	$ 1,919	$ 2,328
Collateralized mortgage obligations | Government National Mortgage Association
Number of Issues
Less than 12 months | issue	2	2
12 months or longer | issue	40	40
Fair Value
Less than 12 months	$ 4,589	$ 7,055
12 months or longer	66,719	72,565
Total	71,308	79,620
Gross Unrealized Loss
Less than 12 months	17	27
12 months or longer	11,551	12,715
Total	$ 11,568	$ 12,742
Collateralized mortgage obligations | Federal Home Loan Mortgage Corporation
Number of Issues
Less than 12 months | issue	0	2
12 months or longer | issue	27	31
Fair Value
Less than 12 months	$ 0	$ 2,589
12 months or longer	51,513	66,361
Total	51,513	68,950
Gross Unrealized Loss
Less than 12 months	0	22
12 months or longer	11,480	13,155
Total	$ 11,480	$ 13,177
Collateralized mortgage obligations | Federal National Mortgage Association
Number of Issues
Less than 12 months | issue	1	2
12 months or longer | issue	20	20
Fair Value
Less than 12 months	$ 2,367	$ 5,454
12 months or longer	30,005	31,460
Total	32,372	36,914
Gross Unrealized Loss
Less than 12 months	4	55
12 months or longer	3,652	4,609
Total	$ 3,656	$ 4,664
Asset-backed securities
Number of Issues
Less than 12 months | issue	7	0
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 16,568	$ 0
12 months or longer	2,476	2,962
Total	19,044	2,962
Gross Unrealized Loss
Less than 12 months	100	0
12 months or longer	26	87
Total	$ 126	$ 87