Summary of Investments - Investments in Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2022 USD ($) issue	Dec. 31, 2021 USD ($) issue
Number of Issues
Less than 12 months | issue	231	97
12 months or longer | issue	31	15
Fair Value
Less than 12 months	$ 548,793	$ 304,080
12 months or longer	97,293	43,871
Total	646,086	347,951
Gross Unrealized Depreciation
Less than 12 months	28,480	7,283
12 months or longer	9,866	1,366
Total	$ 38,346	$ 8,649
U.S. Treasury
Number of Issues
Less than 12 months | issue	6	6
12 months or longer | issue	4	1
Fair Value
Less than 12 months	$ 17,996	$ 32,166
12 months or longer	20,391	2,837
Total	38,387	35,003
Gross Unrealized Depreciation
Less than 12 months	361	630
12 months or longer	1,539	88
Total	$ 1,900	$ 718
U.S. government agency
Number of Issues
Less than 12 months | issue	8	3
12 months or longer | issue	2	0
Fair Value
Less than 12 months	$ 24,482	$ 15,023
12 months or longer	10,846	0
Total	35,328	15,023
Gross Unrealized Depreciation
Less than 12 months	1,008	562
12 months or longer	1,683	0
Total	$ 2,691	$ 562
States, municipalities and political subdivisions | General obligations | Midwest
Number of Issues
Less than 12 months | issue	1
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 7,887
12 months or longer	0
Total	7,887
Gross Unrealized Depreciation
Less than 12 months	42
12 months or longer	0
Total	$ 42
States, municipalities and political subdivisions | General obligations | Northeast
Number of Issues
Less than 12 months | issue	1
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 3,535
12 months or longer	0
Total	3,535
Gross Unrealized Depreciation
Less than 12 months	15
12 months or longer	0
Total	$ 15
States, municipalities and political subdivisions | General obligations | South
Number of Issues
Less than 12 months | issue	4
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 11,122
12 months or longer	0
Total	11,122
Gross Unrealized Depreciation
Less than 12 months	11
12 months or longer	0
Total	$ 11
States, municipalities and political subdivisions | General obligations | West
Number of Issues
Less than 12 months | issue	1
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 7,442
12 months or longer	0
Total	7,442
Gross Unrealized Depreciation
Less than 12 months	14
12 months or longer	0
Total	$ 14
States, municipalities and political subdivisions | Special revenue | Midwest
Number of Issues
Less than 12 months | issue	2
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 3,747
12 months or longer	0
Total	3,747
Gross Unrealized Depreciation
Less than 12 months	26
12 months or longer	0
Total	$ 26
States, municipalities and political subdivisions | Special revenue | Northeast
Number of Issues
Less than 12 months | issue	4
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 12,402
12 months or longer	0
Total	12,402
Gross Unrealized Depreciation
Less than 12 months	142
12 months or longer	0
Total	$ 142
States, municipalities and political subdivisions | Special revenue | South
Number of Issues
Less than 12 months | issue	10	1
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 20,700	$ 1,195
12 months or longer	1,064	0
Total	21,764	1,195
Gross Unrealized Depreciation
Less than 12 months	157	78
12 months or longer	208	0
Total	$ 365	$ 78
States, municipalities and political subdivisions | Special revenue | West
Number of Issues
Less than 12 months | issue	8
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 18,510
12 months or longer	0
Total	18,510
Gross Unrealized Depreciation
Less than 12 months	53
12 months or longer	0
Total	$ 53
Foreign bonds
Number of Issues
Less than 12 months | issue	6	4
12 months or longer | issue	1	1
Fair Value
Less than 12 months	$ 15,455	$ 10,731
12 months or longer	1,795	1,952
Total	17,250	12,683
Gross Unrealized Depreciation
Less than 12 months	1,377	147
12 months or longer	207	50
Total	$ 1,584	$ 197
Public utilities
Number of Issues
Less than 12 months | issue	26	9
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 62,401	$ 24,238
12 months or longer	1,789	0
Total	64,190	24,238
Gross Unrealized Depreciation
Less than 12 months	3,769	481
12 months or longer	210	0
Total	$ 3,979	$ 481
Corporate bonds | Energy
Number of Issues
Less than 12 months | issue	3	1
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 10,626	$ 5,881
12 months or longer	0	0
Total	10,626	5,881
Gross Unrealized Depreciation
Less than 12 months	952	81
12 months or longer	0	0
Total	$ 952	$ 81
Corporate bonds | Industrials
Number of Issues
Less than 12 months | issue	13	4
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 25,751	$ 8,902
12 months or longer	0	0
Total	25,751	8,902
Gross Unrealized Depreciation
Less than 12 months	2,219	162
12 months or longer	0	0
Total	$ 2,219	$ 162
Corporate bonds | Consumer goods and services
Number of Issues
Less than 12 months | issue	16	10
12 months or longer | issue	3	0
Fair Value
Less than 12 months	$ 30,638	$ 26,367
12 months or longer	8,907	0
Total	39,545	26,367
Gross Unrealized Depreciation
Less than 12 months	2,485	611
12 months or longer	1,448	0
Total	$ 3,933	$ 611
Corporate bonds | Health care
Number of Issues
Less than 12 months | issue	3	3
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 19,473	$ 20,550
12 months or longer	0	0
Total	19,473	20,550
Gross Unrealized Depreciation
Less than 12 months	2,496	461
12 months or longer	0	0
Total	$ 2,496	$ 461
Corporate bonds | Technology, media and telecommunications
Number of Issues
Less than 12 months | issue	8	4
12 months or longer | issue	3	1
Fair Value
Less than 12 months	$ 18,827	$ 11,204
12 months or longer	7,056	1,906
Total	25,883	13,110
Gross Unrealized Depreciation
Less than 12 months	1,029	739
12 months or longer	1,852	127
Total	$ 2,881	$ 866
Corporate bonds | Financial services
Number of Issues
Less than 12 months | issue	13	5
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 40,050	$ 13,320
12 months or longer	0	0
Total	40,050	13,320
Gross Unrealized Depreciation
Less than 12 months	2,035	131
12 months or longer	0	0
Total	$ 2,035	$ 131
Mortgage-backed securities
Number of Issues
Less than 12 months | issue	25	12
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 16,224	$ 13,740
12 months or longer	4,397	0
Total	20,621	13,740
Gross Unrealized Depreciation
Less than 12 months	972	229
12 months or longer	338	0
Total	$ 1,310	$ 229
Collateralized mortgage obligations | Federal home loan mortgage corporation
Number of Issues
Less than 12 months | issue	29	11
12 months or longer | issue	9	1
Fair Value
Less than 12 months	$ 65,849	$ 48,256
12 months or longer	31,319	1,032
Total	97,168	49,288
Gross Unrealized Depreciation
Less than 12 months	3,198	1,752
12 months or longer	1,728	20
Total	$ 4,926	$ 1,772
Collateralized mortgage obligations | Federal national mortgage association
Number of Issues
Less than 12 months | issue	13	18
12 months or longer | issue	3	7
Fair Value
Less than 12 months	$ 33,603	$ 50,701
12 months or longer	4,397	30,847
Total	38,000	81,548
Gross Unrealized Depreciation
Less than 12 months	1,643	698
12 months or longer	273	960
Total	$ 1,916	$ 1,658
Collateralized mortgage obligations | Government national mortgage association
Number of Issues
Less than 12 months | issue	31	6
12 months or longer | issue	3	4
Fair Value
Less than 12 months	$ 82,073	$ 21,806
12 months or longer	5,332	5,297
Total	87,405	27,103
Gross Unrealized Depreciation
Less than 12 months	4,476	521
12 months or longer	380	121
Total	$ 4,856	$ 642