Reserve for Losses and Loss Adjustment Expenses - Narrative (Details)		3 Months Ended			6 Months Ended		24 Months Ended
	Mar. 31, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2023 USD ($) portfolio_loss_transfer	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Liability for Claims and Claims Adjustment Expense [Abstract]
Allowance for credit losses on reinsurance recoverables	$ 604,000	$ 670,000	$ 601,000	$ 604,000	$ 670,000	$ 601,000	$ 670,000	$ 661,000	$ 612,000	$ 631,000
Development on prior year loss reserves
Development on prior year loss reserves		2,288,000	(1,576,000)		$ 3,650,000	5,228,000
Number of loss portfolio transfers | portfolio_loss_transfer					2
Funds held		275,331,000			$ 275,331,000		275,331,000		310,953,000
Deferred reinsurance gain		37,572,000			37,572,000		37,572,000		$ 20,091,000
Excess and Surplus Lines
Development on prior year loss reserves
Development on prior year loss reserves		118,000	(32,000)		(206,000)	(91,000)
Excess and Surplus Lines | Commercial Auto Business | Loss Portfolio Transfer
Development on prior year loss reserves
Development on prior year loss reserves		12,600,000			53,600,000		100,300,000
Retroactive reinsurance benefit recognized		14,800,000			44,100,000
Cumulative amounts ceded under loss portfolio transfer		445,400,000			445,400,000		445,400,000
Deferred reinsurance gain		25,200,000			25,200,000		25,200,000
Specialty Admitted Insurance
Development on prior year loss reserves
Development on prior year loss reserves		(839,000)	(1,500,000)		(1,000,000)	(1,500,000)
Casualty Reinsurance
Development on prior year loss reserves
Development on prior year loss reserves		3,000,000	$ 0		4,900,000	$ 6,800,000
Casualty Reinsurance | Loss Portfolio Transfer | Fortitude Reinsurance | JRG Reinsurance Company Ltd
Development on prior year loss reserves
Development on prior year loss reserves		5,800,000		6,800,000	13,700,000
Reinsurance, aggregate coverage limit	400,000,000			400,000,000
Ceded premiums payable	335,000,000			335,000,000
Funds held	310,000,000			$ 310,000,000
Payments for reinsurance	$ 25,000,000
Crediting rate on funds withheld	2.00%
Retroactive reinsurance benefit recognized		2,900,000			5,600,000
Cumulative amounts ceded under loss portfolio transfer		354,700,000			354,700,000		354,700,000
Deferred reinsurance gain		12,400,000			12,400,000		12,400,000
Reinsurance, amount remaining		45,300,000			45,300,000		45,300,000
Excess And Surplus Lines and Casualty Reinsurance | Loss Portfolio Transfer
Development on prior year loss reserves
Development on prior year loss reserves		18,400,000			67,200,000
Retroactive reinsurance benefit recognized		17,800,000			49,800,000
Cumulative amounts ceded under loss portfolio transfer		800,100,000			800,100,000		800,100,000
Deferred reinsurance gain		$ 37,600,000			$ 37,600,000		$ 37,600,000