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Earnings per Share - Additional Information (Detail) - shares
shares in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Equity Option [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Shares excluded from the diluted net income per share 1.7 2.0 0.9
Unvested Stock [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Shares excluded from the diluted net income per share   4.0