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Stock-Based Compensation - Schedule of Information Related to Outstanding SOSARS (Detail) - Stock Only Stock Appreciation Rights (SOSARs) [Member] - $ / shares
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Beginning Balance, Outstanding 2,561,846 2,736,616
Exercised (148,145) (33,050)
Canceled / forfeited (20,994) (17,630)
Ending Balance, Outstanding 2,392,707 2,685,936
Beginning Balance, Weighted Average Exercise Price, Outstanding $ 17.87 $ 17.64
Weighted Average Exercise Price, Exercised 13.26 14.65
Weighted Average Exercise Price, Canceled / forfeited 18.76 18.46
Ending Balance, Weighted Average Exercise Price, Outstanding $ 18.15 $ 17.67