Liability for Unpaid Claims and Claim Adjustment Expenses - Summary of Incurred and Paid Claims Development as Supplementary Information - Credit Property and Casualty (Detail) $ in Thousands	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 995,986
Credit Property and Casualty
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	171,699
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	150,610
All outstanding liabilities before period one, net of reinsurance	0
Liabilities for claims and claim adjustment expenses, net of reinsurance	21,089
Credit Property and Casualty | Accident Year 2018
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	89,308	$ 89,308
IBNR plus expected development	$ 0
Cumulative number of reported claims | claim	31,246
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	$ 89,308	$ 72,693
Credit Property and Casualty | Accident Year 2019
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	82,391
IBNR plus expected development	$ 11,897
Cumulative number of reported claims | claim	23,400
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	$ 61,302