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Stock-Based Compensation (Detail) - shares
12 Months Ended
Dec. 31, 2017
Apr. 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Common stock, shares reserved for future issuance 4,900,000  
2015 Long-Term Incentive Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares authorized   4,800,000
Reduction in number of shares available for issuance due to settlement of stock appreciation rights and stock unit or performance unit award 2  
Reduction in number of shares available for issuance due to settlement of stock option award 1  
Shares available for issuance 4,200,000  
Maximum aggregate shares of common stock subject to stock options, appreciation rights, restricted stock or performance stock unit awards 1,000,000.0  
Stock options | 2015 Long-Term Incentive Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years) 7 years  
Stock options | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 3 years  
Stock options | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 4 years