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Stock-Based Compensation (Valuation and Expense Information) - Additional Information (Detail) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average estimated value $ 5.22 $ 4.28 $ 6.31
Contractual term 10 years    
Weighted average grant date fair value, PSUs granted $ 20.63    
Performance Stock Units (PSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average grant date fair value, PSUs granted $ 23.50 $ 17.64 $ 22.11