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Statutory Financial Information - Additional Information (Detail) - Wright Flood - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Statutory Accounting Practices [Line Items]    
Statutory capital and surplus required $ 7,500,000  
Statutory capital and surplus 31,700,000 $ 28,700,000
Statutory net Income $ 3,000,000.0 $ 4,800,000