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Computation of Earnings Per Share - Additional Information (Detail) - shares
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Stock Options [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Antidilutive shares excluded from calculation of earnings per share 27,000 47,850 35,584 55,350