Reinsurance - Narrative (Details) - USD ($)	Jul. 31, 2019	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2018	Dec. 27, 2018
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable for unpaid claims and claims adjustments		$ 547,975,000	$ 562,845,000
Reinsurance recoverable for unpaid claims and claims adjustments, valuation allowance		0	0
Reinsurance, excess retention, amount reinsured, per policy	$ 2,178,535,000
Reinsurance, amount retained, per policy	600,000,000
Reinsurance recoverable for paid and unpaid claims and claims adjustments, adverse development cover						$ 155,000,000
Reinsurance recoverable for paid and unpaid claims and claims adjustments, ceded cumulative losses	445,000,000
Reinsurance recoverables, including reinsurance premium paid		547,975,000	562,845,000	$ 561,627,000	$ 592,571,000
Deferred gain on retroactive reinsurance		39,270,000	48,960,000
Collateral by third party	445,000,000	424,588,000
Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance recoverables on paid losses, gross		312,786,000
Diversified Reinsurance
Reinsurance Retention Policy [Line Items]
Assets and liabilities associated with reinsurance business retroceded							100.00%
Diversified Reinsurance | Miscellaneous
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable for unpaid claims and claims adjustments		67,181,000	69,006,000
AmTrust Reinsurance
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable for unpaid claims and claims adjustments	$ 445,000,000
Reinsurance recoverables, including reinsurance premium paid		480,138,000	490,860,000
Deferred gain on retroactive reinsurance		$ 35,138,000	$ 45,860,000