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Employee Incentive Plans - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Internally Developed Software    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense, capitalized amount $ 2.2 $ 2.5
PBRSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PBRSU performance period 1 year  
Minimum | PBRSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Performance share target range (percent) 0.00%  
Maximum | PBRSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Performance share target range (percent) 200.00%  
One-half of Grant Vesting in One Year Following Completion of Performance Period [Member] | PBRSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PBRSU vesting period 1 year  
One-half of Grant Vesting in Two Years Following Completion of Performance Period [Member] | PBRSUs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PBRSU vesting period 2 years