Goodwill - Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2020	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Line Items]
Goodwill, gross				$ 210,725
Accumulated impairment losses				(205,225)
Goodwill, net			$ 5,500	5,500	$ 49,610
Goodwill [Roll Forward]
Goodwill, beginning balance			5,500	49,610
Impairment losses	$ (44,100)		0	(44,110)	0
Goodwill, ending balance			5,500	5,500	49,610
Specialty P&C
Goodwill [Line Items]
Goodwill, gross				161,115
Accumulated impairment losses				(161,115)
Goodwill, net				0	0
Goodwill [Roll Forward]
Goodwill, beginning balance			0	0
Impairment losses		$ (161,100)		0
Goodwill, ending balance				0	0
Workers' Compensation Insurance
Goodwill [Line Items]
Goodwill, gross				44,110
Accumulated impairment losses				(44,110)
Goodwill, net				0	44,110
Goodwill [Roll Forward]
Goodwill, beginning balance			0	44,110
Impairment losses	$ (44,100)			(44,110)
Goodwill, ending balance				0	44,110
Segregated Portfolio Cell Reinsurance
Goodwill [Line Items]
Goodwill, gross				5,500
Accumulated impairment losses				0
Goodwill, net				5,500	5,500
Goodwill [Roll Forward]
Goodwill, beginning balance			$ 5,500	5,500
Impairment losses				0
Goodwill, ending balance				$ 5,500	$ 5,500