Reserve for Losses and Loss Adjustment Expenses - Schedule of Incurred Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
E&S – excluding commercial auto | Excess and Surplus Lines
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	$ 2,722,908
All outstanding losses and loss adjustment expenses, net of reinsurance	16,282
E&S – excluding commercial auto | Excess and Surplus Lines | 2016
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	151,612	$ 148,400	$ 141,242	$ 135,491	$ 132,235	$ 125,097	$ 126,971	$ 126,050	$ 125,093	$ 138,507
E&S – excluding commercial auto | Excess and Surplus Lines | 2017
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	158,714	155,593	147,196	134,272	128,674	124,265	132,136	131,897	144,349
E&S – excluding commercial auto | Excess and Surplus Lines | 2018
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	180,931	173,186	167,237	151,563	150,687	146,633	158,458	167,004
E&S – excluding commercial auto | Excess and Surplus Lines | 2019
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	237,568	228,076	204,844	188,061	189,671	194,759	214,653
E&S – excluding commercial auto | Excess and Surplus Lines | 2020
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	296,540	273,883	231,658	207,210	211,732	239,897
E&S – excluding commercial auto | Excess and Surplus Lines | 2021
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	321,722	307,338	274,120	286,343	304,435
E&S – excluding commercial auto | Excess and Surplus Lines | 2022
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	342,533	320,146	293,402	340,436
E&S – excluding commercial auto | Excess and Surplus Lines | 2023
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	335,617	330,330	369,255
E&S – excluding commercial auto | Excess and Surplus Lines | 2024
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	345,686	360,426
E&S – excluding commercial auto | Excess and Surplus Lines | 2025
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	351,985
Commercial Auto | Excess and Surplus Lines
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	1,446,115
All outstanding losses and loss adjustment expenses, net of reinsurance	113
Commercial Auto | Excess and Surplus Lines | Commercial Auto LPT
Claims Development [Line Items]
All outstanding losses and loss adjustment expenses, net of reinsurance	59,531
Commercial Auto | Excess and Surplus Lines | 2016
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	165,286	165,121	165,744	164,046	164,399	157,712	147,122	126,791	109,286	74,340
Commercial Auto | Excess and Surplus Lines | 2017
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	374,566	376,306	376,251	366,636	355,713	319,472	272,421	208,743	207,355
Commercial Auto | Excess and Surplus Lines | 2018
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	387,645	389,261	389,244	371,637	349,067	283,408	230,220	255,881
Commercial Auto | Excess and Surplus Lines | 2019
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	413,077	416,654	408,340	365,279	339,771	240,773	262,306
Commercial Auto | Excess and Surplus Lines | 2020
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	22,927	22,062	19,009	12,324	10,899	19,133
Commercial Auto | Excess and Surplus Lines | 2021
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	20,774	19,998	17,319	16,565	21,154
Commercial Auto | Excess and Surplus Lines | 2022
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	21,370	19,730	19,921	26,126
Commercial Auto | Excess and Surplus Lines | 2023
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	16,879	16,089	18,181
Commercial Auto | Excess and Surplus Lines | 2024
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	12,491	11,602
Commercial Auto | Excess and Surplus Lines | 2025
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	11,100
Individual Risk Workers' Compensation | Specialty Admitted Insurance
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	128,246
All outstanding losses and loss adjustment expenses, net of reinsurance	376
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2016
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	12,484	12,502	12,510	12,790	13,069	14,050	15,800	18,050	20,299	21,678
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2017
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	15,311	15,318	15,360	15,487	16,606	18,810	19,779	22,071	24,869
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2018
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	11,894	11,793	11,829	12,139	14,200	16,038	16,288	16,432
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2019
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	17,257	17,408	17,624	18,129	20,631	21,056	20,253
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2020
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	18,235	18,617	18,934	19,389	22,240	20,137
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2021
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	12,472	12,702	12,668	14,713	14,519
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2022
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	11,439	11,096	11,828	14,507
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2023
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	19,118	19,218	21,095
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2024
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	9,760	12,715
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2025
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	276
Fronting and Programs | Specialty Admitted Insurance
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	361,913
All outstanding losses and loss adjustment expenses, net of reinsurance	92
Fronting and Programs | Specialty Admitted Insurance | 2016
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	13,336	13,133	13,289	14,304	15,090	14,468	15,522	14,682	15,670	$ 11,542
Fronting and Programs | Specialty Admitted Insurance | 2017
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	23,185	23,576	23,128	24,893	25,097	24,728	25,201	24,271	$ 21,229
Fronting and Programs | Specialty Admitted Insurance | 2018
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	19,021	19,129	19,193	19,268	20,158	19,822	20,677	$ 21,758
Fronting and Programs | Specialty Admitted Insurance | 2019
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	18,196	18,210	18,777	18,956	19,991	19,020	$ 18,832
Fronting and Programs | Specialty Admitted Insurance | 2020
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	35,930	34,650	34,705	31,555	28,131	$ 25,433
Fronting and Programs | Specialty Admitted Insurance | 2021
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	47,995	46,526	47,505	44,857	$ 39,999
Fronting and Programs | Specialty Admitted Insurance | 2022
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	49,139	50,544	51,101	$ 47,262
Fronting and Programs | Specialty Admitted Insurance | 2023
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	62,761	58,449	$ 53,635
Fronting and Programs | Specialty Admitted Insurance | 2024
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	56,860	$ 55,536
Fronting and Programs | Specialty Admitted Insurance | 2025
Claims Development [Line Items]
Incurred losses and loss adjustment expenses, net of reinsurance	$ 35,490