Summary of Investments - Investments in Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2022 USD ($) issue	Dec. 31, 2021 USD ($) issue
Number of Issues
Less than 12 months | issue	478	97
12 months or longer | issue	39	15
Fair Value
Less than 12 months	$ 1,038,136	$ 304,080
12 months or longer	96,025	43,871
Total	1,134,161	347,951
Gross Unrealized Depreciation
Less than 12 months	60,729	7,283
12 months or longer	14,366	1,366
Total	$ 75,095	$ 8,649
U.S. Treasury
Number of Issues
Less than 12 months | issue	5	6
12 months or longer | issue	4	1
Fair Value
Less than 12 months	$ 7,557	$ 32,166
12 months or longer	7,279	2,837
Total	14,836	35,003
Gross Unrealized Depreciation
Less than 12 months	168	630
12 months or longer	575	88
Total	$ 743	$ 718
U.S. government agency
Number of Issues
Less than 12 months | issue	17	3
12 months or longer | issue	2	0
Fair Value
Less than 12 months	$ 55,985	$ 15,023
12 months or longer	10,110	0
Total	66,095	15,023
Gross Unrealized Depreciation
Less than 12 months	2,582	562
12 months or longer	2,362	0
Total	$ 4,944	$ 562
States, municipalities and political subdivisions | General obligations | Midwest
Number of Issues
Less than 12 months | issue	8
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 19,825
12 months or longer	0
Total	19,825
Gross Unrealized Depreciation
Less than 12 months	217
12 months or longer	0
Total	$ 217
States, municipalities and political subdivisions | General obligations | Northeast
Number of Issues
Less than 12 months | issue	2
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 6,021
12 months or longer	0
Total	6,021
Gross Unrealized Depreciation
Less than 12 months	66
12 months or longer	0
Total	$ 66
States, municipalities and political subdivisions | General obligations | South
Number of Issues
Less than 12 months | issue	18
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 37,889
12 months or longer	0
Total	37,889
Gross Unrealized Depreciation
Less than 12 months	677
12 months or longer	0
Total	$ 677
States, municipalities and political subdivisions | General obligations | West
Number of Issues
Less than 12 months | issue	11
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 32,924
12 months or longer	0
Total	32,924
Gross Unrealized Depreciation
Less than 12 months	458
12 months or longer	0
Total	$ 458
States, municipalities and political subdivisions | Special revenue | Midwest
Number of Issues
Less than 12 months | issue	24
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 48,534
12 months or longer	0
Total	48,534
Gross Unrealized Depreciation
Less than 12 months	630
12 months or longer	0
Total	$ 630
States, municipalities and political subdivisions | Special revenue | Northeast
Number of Issues
Less than 12 months | issue	14
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 37,923
12 months or longer	0
Total	37,923
Gross Unrealized Depreciation
Less than 12 months	943
12 months or longer	0
Total	$ 943
States, municipalities and political subdivisions | Special revenue | South
Number of Issues
Less than 12 months | issue	44	1
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 99,360	$ 1,195
12 months or longer	902	0
Total	100,262	1,195
Gross Unrealized Depreciation
Less than 12 months	2,539	78
12 months or longer	369	0
Total	$ 2,908	$ 78
States, municipalities and political subdivisions | Special revenue | West
Number of Issues
Less than 12 months | issue	26
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 68,625
12 months or longer	0
Total	68,625
Gross Unrealized Depreciation
Less than 12 months	1,899
12 months or longer	0
Total	$ 1,899
Foreign bonds
Number of Issues
Less than 12 months | issue	11	4
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 24,657	$ 10,731
12 months or longer	1,584	1,952
Total	26,241	12,683
Gross Unrealized Depreciation
Less than 12 months	2,606	147
12 months or longer	418	50
Total	$ 3,024	$ 197
Public utilities
Number of Issues
Less than 12 months | issue	48	9
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 112,236	$ 24,238
12 months or longer	1,734	0
Total	113,970	24,238
Gross Unrealized Depreciation
Less than 12 months	8,657	481
12 months or longer	265	0
Total	$ 8,922	$ 481
Corporate bonds | Energy
Number of Issues
Less than 12 months | issue	16	1
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 35,237	$ 5,881
12 months or longer	0	0
Total	35,237	5,881
Gross Unrealized Depreciation
Less than 12 months	2,281	81
12 months or longer	0	0
Total	$ 2,281	$ 81
Corporate bonds | Industrials
Number of Issues
Less than 12 months | issue	20	4
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 44,581	$ 8,902
12 months or longer	0	0
Total	44,581	8,902
Gross Unrealized Depreciation
Less than 12 months	4,442	162
12 months or longer	0	0
Total	$ 4,442	$ 162
Corporate bonds | Consumer goods and services
Number of Issues
Less than 12 months | issue	24	10
12 months or longer | issue	3	0
Fair Value
Less than 12 months	$ 56,668	$ 26,367
12 months or longer	7,946	0
Total	64,614	26,367
Gross Unrealized Depreciation
Less than 12 months	5,223	611
12 months or longer	2,399	0
Total	$ 7,622	$ 611
Corporate bonds | Health care
Number of Issues
Less than 12 months | issue	10	3
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 24,077	$ 20,550
12 months or longer	0	0
Total	24,077	20,550
Gross Unrealized Depreciation
Less than 12 months	4,203	461
12 months or longer	0	0
Total	$ 4,203	$ 461
Corporate bonds | Technology, media and telecommunications
Number of Issues
Less than 12 months | issue	21	4
12 months or longer | issue	3	1
Fair Value
Less than 12 months	$ 45,293	$ 11,204
12 months or longer	6,146	1,906
Total	51,439	13,110
Gross Unrealized Depreciation
Less than 12 months	2,862	739
12 months or longer	2,756	127
Total	$ 5,618	$ 866
Corporate bonds | Financial services
Number of Issues
Less than 12 months | issue	39	5
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 100,592	$ 13,320
12 months or longer	0	0
Total	100,592	13,320
Gross Unrealized Depreciation
Less than 12 months	5,696	131
12 months or longer	0	0
Total	$ 5,696	$ 131
Mortgage-backed securities
Number of Issues
Less than 12 months | issue	39	12
12 months or longer | issue	4	0
Fair Value
Less than 12 months	$ 8,696	$ 13,740
12 months or longer	10,773	0
Total	19,469	13,740
Gross Unrealized Depreciation
Less than 12 months	695	229
12 months or longer	1,258	0
Total	$ 1,953	$ 229
Collateralized mortgage obligations | Federal home loan mortgage corporation
Number of Issues
Less than 12 months | issue	28	11
12 months or longer | issue	14	1
Fair Value
Less than 12 months	$ 49,737	$ 48,256
12 months or longer	40,471	1,032
Total	90,208	49,288
Gross Unrealized Depreciation
Less than 12 months	4,325	1,752
12 months or longer	3,103	20
Total	$ 7,428	$ 1,772
Collateralized mortgage obligations | Federal national mortgage association
Number of Issues
Less than 12 months | issue	16	18
12 months or longer | issue	3	7
Fair Value
Less than 12 months	$ 35,968	$ 50,701
12 months or longer	4,033	30,847
Total	40,001	81,548
Gross Unrealized Depreciation
Less than 12 months	2,553	698
12 months or longer	321	960
Total	$ 2,874	$ 1,658
Collateralized mortgage obligations | Government national mortgage association
Number of Issues
Less than 12 months | issue	36	6
12 months or longer | issue	3	4
Fair Value
Less than 12 months	$ 82,222	$ 21,806
12 months or longer	5,047	5,297
Total	87,269	27,103
Gross Unrealized Depreciation
Less than 12 months	6,914	521
12 months or longer	540	121
Total	$ 7,454	$ 642
Asset-backed securities
Number of Issues
Less than 12 months | issue	1
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 3,529
12 months or longer	0
Total	3,529
Gross Unrealized Depreciation
Less than 12 months	93
12 months or longer	0
Total	$ 93