Reconciliation of Net Incurred and Paid Claims Development Tables to Liability for Unpaid Losses and Loss Adjustment Expenses in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 528,899
Reinsurance recoverable on unpaid claims	74,251
Total other outstanding liabilities	27,031
Total gross liability for unpaid losses and loss adjustment expenses	630,181	$ 680,031	$ 634,664	$ 651,042
Commercial Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Ceded Allowance	8,992
Unallocated claims adjustment expenses	15,707
Purchase accounting adjustment	(400)
Loss Clearing	(1,939)
Commercial Specialty | Property Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	33,651
Reinsurance recoverable on unpaid claims	12,472
Commercial Specialty | Casualty Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	274,535
Reinsurance recoverable on unpaid claims	47,130
Specialty Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unallocated claims adjustment expenses	1,074
Loss Clearing	1
Fronted business ceded to Assurant	2,421
Specialty Property | Property Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	24,350
Reinsurance recoverable on unpaid claims	6,219
Specialty Property | Casualty Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	14,819
Reinsurance recoverable on unpaid claims	1,450
Farm, Ranch & Stable
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Ceded Allowance	0
Unallocated claims adjustment expenses	1,040
Loss Clearing	0
Farm, Ranch & Stable | Property Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	8,849
Reinsurance recoverable on unpaid claims	563
Farm, Ranch & Stable | Casualty Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	28,733
Reinsurance recoverable on unpaid claims	6,417
Reinsurance Operations
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unallocated claims adjustment expenses	365
Other	(230)
Reinsurance Operations | Property Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	109,257
Reinsurance recoverable on unpaid claims	0
Reinsurance Operations | Casualty Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	34,705
Reinsurance recoverable on unpaid claims	$ 0