Statutory Financial Information - Additional Information (Detail) - Wright Flood - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Statutory Accounting Practices [Line Items]
Statutory capital and surplus required	$ 7,500,000
Statutory capital and surplus	22,800,000	$ 28,700,000
Statutory net Income	$ 4,300,000	$ 4,800,000