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Stock-based Compensation Plans - Additional Information 1 (Detail)
12 Months Ended
Dec. 31, 2018
Award
shares
Dec. 31, 2017
shares
Dec. 31, 2016
shares
Dec. 31, 2015
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period 1 year      
Restricted Stock Equity Awards        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period 3 years 3 years 3 years  
Performance Share        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period 3 years      
Number of awards available for grant 3      
Performance Share | Common Stock        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of share value each unit represents at grant date | shares 1      
Performance-based PG-PSUs and RG-PSUs        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period 3 years      
Number of awards available for grant 2      
Performance-based PG-PSUs and RG-PSUs | Minimum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Potential payout of shares granted 0.00%      
Performance-based PG-PSUs and RG-PSUs | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Potential payout of shares granted 200.00%      
Performance Based TSR - PSUs        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period 3 years      
Number of awards available for grant 1      
Performance Based TSR - PSUs | Minimum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Potential payout of shares granted 0.00% 0.00% 0.00%  
Performance Based TSR - PSUs | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Potential payout of shares granted 200.00% 150.00% 150.00%  
Stock Appreciation Rights (SARs)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of stock option outstanding | shares 1,104 382,779 1,003,600 1,510,977