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Earnings Per Share - Additional Information (Detail) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Earnings per share [line items]      
Description of types of warranties Multiplying it by 15    
Anti-dilutive instruments 3,309,539 2,360,945 2,033,768
Common Shares [member]      
Earnings per share [line items]      
Weighted average number of shares outstanding 24,757,176 24,454,850 21,522,342