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Stock-Based Compensation (PSUs, RSUs and Restricted Stock) - Additional Information (Detail) - USD ($)
shares in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PSU shares grant approved by board of directors 8  
Stock-based compensation expense $ 1,819,000 $ 1,883,000
Performance Stock Units (PSUs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PSU shares grant approved by board of directors   500
Market-Based PSUs, RSUs and Restricted Stock [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to other than options $ 12,900,000  
Recognition period of unvested compensation expense 2 years 10 months 24 days  
Performance-Based PSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to other than options $ 10,700,000  
Recognition period of unvested compensation expense 3 years  
Performance-Based PSU Awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense $ 0