Summary of Investments - Fixed Maturities Unrealized Loss (Details) $ in Thousands	Mar. 31, 2024 USD ($) issue	Dec. 31, 2023 USD ($) issue
Number of Issues
Less than 12 months | issue	153	137
12 months or longer | issue	469	459
Fair Value
Less than 12 months	$ 375,872	$ 285,342
12 months or longer	951,841	960,788
Total	1,327,713	1,246,130
Gross Unrealized Loss
Less than 12 months	3,064	1,608
12 months or longer	93,099	89,740
Total	$ 96,163	$ 91,348
U.S. Treasury
Number of Issues
Less than 12 months | issue	4	2
12 months or longer | issue	6	6
Fair Value
Less than 12 months	$ 28,933	$ 4,138
12 months or longer	12,726	12,717
Total	41,659	16,855
Gross Unrealized Loss
Less than 12 months	132	46
12 months or longer	582	629
Total	$ 714	$ 675
U.S. government agency
Number of Issues
Less than 12 months | issue	3	3
12 months or longer | issue	23	23
Fair Value
Less than 12 months	$ 8,940	$ 10,986
12 months or longer	70,702	71,375
Total	79,642	82,361
Gross Unrealized Loss
Less than 12 months	56	14
12 months or longer	8,908	8,288
Total	$ 8,964	$ 8,302
General obligations | Midwest
Number of Issues
Less than 12 months | issue	11	11
12 months or longer | issue	6	3
Fair Value
Less than 12 months	$ 16,175	$ 19,534
12 months or longer	16,922	10,737
Total	33,097	30,271
Gross Unrealized Loss
Less than 12 months	79	61
12 months or longer	228	76
Total	$ 307	$ 137
General obligations | Northeast
Number of Issues
Less than 12 months | issue	6	3
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 3,624	$ 5,371
12 months or longer	3,463	3,469
Total	7,087	8,840
Gross Unrealized Loss
Less than 12 months	7	8
12 months or longer	34	35
Total	$ 41	$ 43
General obligations | South
Number of Issues
Less than 12 months | issue	10	12
12 months or longer | issue	11	9
Fair Value
Less than 12 months	$ 19,982	$ 21,753
12 months or longer	20,677	16,610
Total	40,659	38,363
Gross Unrealized Loss
Less than 12 months	177	91
12 months or longer	421	309
Total	$ 598	$ 400
General obligations | West
Number of Issues
Less than 12 months | issue	17	17
12 months or longer | issue	10	7
Fair Value
Less than 12 months	$ 38,938	$ 38,204
12 months or longer	25,487	20,064
Total	64,425	58,268
Gross Unrealized Loss
Less than 12 months	177	140
12 months or longer	413	331
Total	$ 590	$ 471
Special revenue | Midwest
Number of Issues
Less than 12 months | issue	11	17
12 months or longer | issue	15	11
Fair Value
Less than 12 months	$ 18,084	$ 29,535
12 months or longer	29,692	23,375
Total	47,776	52,910
Gross Unrealized Loss
Less than 12 months	146	113
12 months or longer	267	245
Total	$ 413	$ 358
Special revenue | Northeast
Number of Issues
Less than 12 months | issue	5	6
12 months or longer | issue	10	8
Fair Value
Less than 12 months	$ 15,071	$ 15,131
12 months or longer	27,206	24,271
Total	42,277	39,402
Gross Unrealized Loss
Less than 12 months	70	67
12 months or longer	568	493
Total	$ 638	$ 560
Special revenue | South
Number of Issues
Less than 12 months | issue	22	21
12 months or longer | issue	37	32
Fair Value
Less than 12 months	$ 48,147	$ 45,639
12 months or longer	76,664	66,925
Total	124,811	112,564
Gross Unrealized Loss
Less than 12 months	334	232
12 months or longer	2,304	1,923
Total	$ 2,638	$ 2,155
Special revenue | West
Number of Issues
Less than 12 months | issue	24	20
12 months or longer | issue	20	16
Fair Value
Less than 12 months	$ 36,615	$ 32,789
12 months or longer	46,373	38,495
Total	82,988	71,284
Gross Unrealized Loss
Less than 12 months	294	248
12 months or longer	772	588
Total	$ 1,066	$ 836
Foreign bonds
Number of Issues
Less than 12 months | issue	0	0
12 months or longer | issue	6	9
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	12,176	19,172
Total	12,176	19,172
Gross Unrealized Loss
Less than 12 months	0	0
12 months or longer	1,093	2,083
Total	$ 1,093	$ 2,083
Public utilities
Number of Issues
Less than 12 months | issue	4	4
12 months or longer | issue	48	48
Fair Value
Less than 12 months	$ 10,305	$ 7,151
12 months or longer	108,152	111,793
Total	118,457	118,944
Gross Unrealized Loss
Less than 12 months	169	74
12 months or longer	10,598	9,980
Total	$ 10,767	$ 10,054
Corporate bonds | Energy
Number of Issues
Less than 12 months | issue	0	0
12 months or longer | issue	13	15
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	31,746	34,331
Total	31,746	34,331
Gross Unrealized Loss
Less than 12 months	0	0
12 months or longer	2,220	2,127
Total	$ 2,220	$ 2,127
Corporate bonds | Industrials
Number of Issues
Less than 12 months | issue	2	1
12 months or longer | issue	19	21
Fair Value
Less than 12 months	$ 4,143	$ 1,210
12 months or longer	40,544	47,462
Total	44,687	48,672
Gross Unrealized Loss
Less than 12 months	74	19
12 months or longer	4,845	4,920
Total	$ 4,919	$ 4,939
Corporate bonds | Consumer goods and services
Number of Issues
Less than 12 months | issue	5	4
12 months or longer | issue	26	28
Fair Value
Less than 12 months	$ 17,465	$ 14,724
12 months or longer	63,446	68,837
Total	80,911	83,561
Gross Unrealized Loss
Less than 12 months	323	98
12 months or longer	7,902	7,567
Total	$ 8,225	$ 7,665
Corporate bonds | Health care
Number of Issues
Less than 12 months | issue	1	1
12 months or longer | issue	10	11
Fair Value
Less than 12 months	$ 2,932	$ 3,000
12 months or longer	23,174	26,544
Total	26,106	29,544
Gross Unrealized Loss
Less than 12 months	69	2
12 months or longer	4,568	4,497
Total	$ 4,637	$ 4,499
Corporate bonds | Technology, media and telecommunications
Number of Issues
Less than 12 months | issue	3	1
12 months or longer | issue	26	27
Fair Value
Less than 12 months	$ 9,794	$ 3,969
12 months or longer	59,197	62,988
Total	68,991	66,957
Gross Unrealized Loss
Less than 12 months	216	35
12 months or longer	6,499	5,630
Total	$ 6,715	$ 5,665
Corporate bonds | Financial services
Number of Issues
Less than 12 months | issue	4	5
12 months or longer | issue	39	44
Fair Value
Less than 12 months	$ 12,261	$ 14,327
12 months or longer	97,549	112,517
Total	109,810	126,844
Gross Unrealized Loss
Less than 12 months	308	223
12 months or longer	5,990	7,158
Total	$ 6,298	$ 7,381
Mortgage-backed securities
Number of Issues
Less than 12 months | issue	4	3
12 months or longer | issue	50	48
Fair Value
Less than 12 months	$ 35,406	$ 2,783
12 months or longer	17,792	15,758
Total	53,198	18,541
Gross Unrealized Loss
Less than 12 months	138	33
12 months or longer	2,530	2,295
Total	$ 2,668	$ 2,328
Collateralized mortgage obligations | Government National Mortgage Association
Number of Issues
Less than 12 months | issue	10	2
12 months or longer | issue	41	40
Fair Value
Less than 12 months	$ 35,428	$ 7,055
12 months or longer	72,010	72,565
Total	107,438	79,620
Gross Unrealized Loss
Less than 12 months	140	27
12 months or longer	13,599	12,715
Total	$ 13,739	$ 12,742
Collateralized mortgage obligations | Federal Home Loan Mortgage Corporation
Number of Issues
Less than 12 months | issue	2	2
12 months or longer | issue	31	31
Fair Value
Less than 12 months	$ 5,152	$ 2,589
12 months or longer	63,729	66,361
Total	68,881	68,950
Gross Unrealized Loss
Less than 12 months	6	22
12 months or longer	13,765	13,155
Total	$ 13,771	$ 13,177
Collateralized mortgage obligations | Federal National Mortgage Association
Number of Issues
Less than 12 months | issue	4	2
12 months or longer | issue	20	20
Fair Value
Less than 12 months	$ 8,201	$ 5,454
12 months or longer	29,629	31,460
Total	37,830	36,914
Gross Unrealized Loss
Less than 12 months	78	55
12 months or longer	4,911	4,609
Total	$ 4,989	$ 4,664
Asset-backed securities
Number of Issues
Less than 12 months | issue	1	0
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 276	$ 0
12 months or longer	2,785	2,962
Total	3,061	2,962
Gross Unrealized Loss
Less than 12 months	71	0
12 months or longer	82	87
Total	$ 153	$ 87