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Earnings Per Share - Additional Information (Detail) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock Compensation Plans [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Options to purchase common stock, Shares 126,000 140,000 489,000