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Stock-Based Compensation (PSUs, RSUs and Restricted Stock) - Additional Information (Detail) - USD ($)
shares in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
PSU shares grant approved by board of directors   950    
Recognition period of unvested compensation expense   2 years 10 months 24 days    
Stock-based compensation expense   $ 7,433,000 $ 6,695,000 $ 6,712,000
Performance Stock Units (PSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
PSU shares grant approved by board of directors 500      
Performance Stock Units (PSUs) [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of performance stock units granted   0.00%    
Performance Stock Units (PSUs) [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of performance stock units granted   150.00%    
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
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   $ 13,900,000    
Recognition period of unvested compensation expense   3 years 2 months 12 days    
Performance-Based PSUs [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation expense related to other than options   $ 11,400,000    
Recognition period of unvested compensation expense   3 years    
Stock-based compensation expense   $ 0