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Share-Based Compensation - Narrative (Detail)
$ / shares in Units, $ in Thousands
2 Months Ended 12 Months Ended
Feb. 28, 2019
shares
Dec. 31, 2018
USD ($)
plan
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of stock-based compensation plans | plan   3    
Award vesting period       10 years
Compensation expense | $   $ 6,111 $ 10,888 $ 5,456
Compensation cost related to nonvested management incentive plan shares, performance shares, and restricted stock/units not yet recognized | $   $ 4,000    
Compensation cost not yet recognized, period for recognition   1 year 6 months    
Management Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   3 years    
Number of shares, granted (in shares)   0    
Weighted average grant date fair value (in USD per share) | $ / shares   $ 85.44 $ 59.05
Restricted Stock/Unit Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares, granted (in shares)   77,000    
Weighted average grant date fair value (in USD per share) | $ / shares   $ 69.16 $ 85.39 $ 60.39
Restricted Stock/Unit Plan | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares, granted (in shares) 0      
Restricted Stock/Unit Plan | Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares, granted (in shares)   34,000    
Performance measurement period   3 years    
Compensation expense | $   $ 2,100 $ 1,200  
Vesting Tranche One | Restricted Stock/Unit Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting percentage   40.00%    
Vesting Tranche Two | Restricted Stock/Unit Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting percentage   30.00%    
Vesting Tranche Three | Restricted Stock/Unit Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting percentage   30.00%