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Weighted Average Common Shares - Additional Information (Detail) - shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Anti-dilutive awards excluded from computations of diluted earnings per share 0 0  
Employee Stock Option [Member]      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Anti-dilutive awards excluded from computations of diluted earnings per share     2,400
Common Stock [Member]      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average number of shares issued 37 64 143