Statutory Financial Information - Additional Information (Detail) - Wright Flood - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Statutory capital and surplus required	$ 7,500,000
Statutory capital and surplus	26,700,000	$ 23,500,000
Statutory net Income	$ 2,900,000	$ 8,200,000