Reserve for Losses and Loss Adjustment Expenses -Schedule of Cumulative Paid Losses and Loss Adjustment Expenses (Details) $ in Thousands	Dec. 31, 2025 USD ($) claim	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Claims Development [Line Items]
Reinsurance recoverable on unpaid losses, net	$ 2,026,110	$ 1,996,913
Excess and Surplus Lines | E&S ADC
Claims Development [Line Items]
Reinsurance recoverable on unpaid losses, net	0	313,242	$ 0
E&S – excluding commercial auto | Excess and Surplus Lines
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	1,390,402
All outstanding losses and loss adjustment expenses, net of reinsurance	$ 16,282
Claims outstanding | claim	117
Total outstanding losses and loss adjustment expenses, net of reinsurance	$ 914,226
E&S – excluding commercial auto | Excess and Surplus Lines | E&S ADC
Claims Development [Line Items]
All outstanding losses and loss adjustment expenses, net of reinsurance	1,332,506
Reinsurance recoverable on unpaid losses, net	434,562
E&S – excluding commercial auto | Excess and Surplus Lines | 2016
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	141,710	133,928	126,916	$ 116,059	$ 102,072	$ 90,166	$ 70,105	$ 46,045	$ 22,852	$ 5,180
E&S – excluding commercial auto | Excess and Surplus Lines | 2017
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	141,347	132,182	120,229	102,866	81,303	64,924	42,764	22,956	5,290
E&S – excluding commercial auto | Excess and Surplus Lines | 2018
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	155,337	138,319	124,903	105,538	76,494	50,679	26,160	6,000
E&S – excluding commercial auto | Excess and Surplus Lines | 2019
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	191,455	166,472	136,289	103,836	62,227	31,346	8,235
E&S – excluding commercial auto | Excess and Surplus Lines | 2020
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	211,509	168,550	117,892	73,106	34,561	8,642
E&S – excluding commercial auto | Excess and Surplus Lines | 2021
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	204,642	154,168	100,649	55,070	11,693
E&S – excluding commercial auto | Excess and Surplus Lines | 2022
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	177,429	108,960	51,537	12,713
E&S – excluding commercial auto | Excess and Surplus Lines | 2023
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	109,278	49,094	10,927
E&S – excluding commercial auto | Excess and Surplus Lines | 2024
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	48,871	11,096
E&S – excluding commercial auto | Excess and Surplus Lines | 2025
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	8,824
Commercial Auto | Excess and Surplus Lines
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	1,386,584
All outstanding losses and loss adjustment expenses, net of reinsurance	$ 113
Claims outstanding | claim	0
Total outstanding losses and loss adjustment expenses, net of reinsurance	$ 34,256
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
Reinsurance recoverable on unpaid losses, net	11,520
Commercial Auto | Excess and Surplus Lines | E&S ADC
Claims Development [Line Items]
Reinsurance recoverable on unpaid losses, net	13,868
Commercial Auto | Excess and Surplus Lines | 2016
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	165,091	164,491	162,219	158,819	152,030	141,545	125,108	89,381	54,054	18,295
Commercial Auto | Excess and Surplus Lines | 2017
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	373,717	369,931	364,501	344,235	309,860	252,169	192,961	107,377	41,467
Commercial Auto | Excess and Surplus Lines | 2018
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	384,415	379,246	368,865	329,009	257,346	184,686	119,099	45,136
Commercial Auto | Excess and Surplus Lines | 2019
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	402,253	393,141	358,920	285,725	192,982	107,182	44,225
Commercial Auto | Excess and Surplus Lines | 2020
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	19,129	17,705	14,151	7,304	2,854	628
Commercial Auto | Excess and Surplus Lines | 2021
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	17,072	12,936	10,325	4,313	2,810
Commercial Auto | Excess and Surplus Lines | 2022
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	12,994	8,691	5,365	1,897
Commercial Auto | Excess and Surplus Lines | 2023
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	10,195	5,341	2,066
Commercial Auto | Excess and Surplus Lines | 2024
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	1,165	319
Commercial Auto | Excess and Surplus Lines | 2025
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	553
Individual Risk Workers' Compensation | Specialty Admitted Insurance
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	120,603
All outstanding losses and loss adjustment expenses, net of reinsurance	376
Outstanding losses and loss adjustment expenses assumed from involuntary workers’ compensation pools	$ 2,198
Claims outstanding | claim	2
Total outstanding losses and loss adjustment expenses, net of reinsurance	$ 10,217
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2016
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	12,483	12,483	12,483	12,483	12,483	12,481	12,432	12,135	10,227	4,664
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2017
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	15,295	15,286	15,279	15,236	15,210	15,195	14,285	12,782	6,546
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2018
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	11,752	11,747	11,752	11,765	11,746	11,412	9,034	4,497
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2019
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	17,224	17,179	17,154	16,909	16,254	13,776	5,473
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2020
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	17,657	17,606	17,206	16,665	14,668	7,394
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2021
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	12,085	11,865	11,679	10,780	5,874
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2022
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	10,518	10,348	9,732	5,943
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2023
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	15,610	12,764	6,126
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2024
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	7,977	4,998
Individual Risk Workers' Compensation | Specialty Admitted Insurance | 2025
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	2
Fronting and Programs | Specialty Admitted Insurance
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	250,869
All outstanding losses and loss adjustment expenses, net of reinsurance	92
Outstanding losses and loss adjustment expenses assumed from involuntary workers’ compensation pools	$ 1,864
Claims outstanding | claim	2
Total outstanding losses and loss adjustment expenses, net of reinsurance	$ 113,000
Fronting and Programs | Specialty Admitted Insurance | 2016
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	12,794	12,567	12,321	12,142	11,711	10,896	10,732	6,888	5,123	$ 1,894
Fronting and Programs | Specialty Admitted Insurance | 2017
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	22,268	21,752	20,770	20,655	18,219	15,854	13,065	6,682	$ 1,223
Fronting and Programs | Specialty Admitted Insurance | 2018
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	16,733	16,457	15,424	14,059	12,631	10,495	4,972	$ 885
Fronting and Programs | Specialty Admitted Insurance | 2019
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	16,203	15,740	14,914	13,007	9,958	5,125	$ 4,358
Fronting and Programs | Specialty Admitted Insurance | 2020
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	31,683	29,084	26,523	20,903	15,678	$ 5,375
Fronting and Programs | Specialty Admitted Insurance | 2021
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	39,295	34,120	27,156	18,106	$ 8,347
Fronting and Programs | Specialty Admitted Insurance | 2022
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	36,354	30,131	23,284	$ 13,018
Fronting and Programs | Specialty Admitted Insurance | 2023
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	38,368	26,983	$ 13,145
Fronting and Programs | Specialty Admitted Insurance | 2024
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	28,812	$ 14,745
Fronting and Programs | Specialty Admitted Insurance | 2025
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	$ 8,359