Statutory Financial Information - Additional Information (Detail) - Wright Flood - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Statutory Accounting Practices [Line Items]
Statutory capital and surplus required	$ 7,500,000
Statutory capital and surplus	30,200,000	$ 28,700,000
Statutory net Income	$ 1,500,000	$ 4,800,000