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Share-Based Compensation - Activity in Company's Plan - Long Term Incentive Plan (Detail) - Long Term Incentive Plan Stock Option [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at January 1, 2019, Number of Shares 30,750    
Granted, Number of Shares 5,000 5,000 5,000
Exercised, Number of Shares (4,000) (3,500) (28,500)
Forfeited, Number of Shares 0    
Outstanding (vested and expected to vest) at December 31, 2019, Number of Shares 31,750    
Exercisable at December 31, 2019, Number of Shares 23,000    
Outstanding at January 1, 2019, Weighted Average Exercise Price per Share $ 56.81    
Granted, Weighted Average Exercise Price per Share 60.60    
Exercised, Weighted Average Exercise Price per Share 45.96    
Forfeited, Weighted Average Exercise Price per Share 0.00    
Outstanding (vested and expected to vest) at December 31, 2019, Weighted Average Exercise Price per Share 58.77    
Exercisable at December 31, 2019, Weighted Average Exercise Price per Share $ 58.68    
Outstanding (vested and expected to vest) at December 31, 2019, Weighted Average Remaining Contractual Term 6 years 7 months 6 days    
Exercisable at December 31, 2019, Weighted Average Remaining Contractual Term 5 years 7 months 6 days    
Outstanding (vested and expected to vest) at December 31, 2019, Aggregate Intrinsic Value $ 169    
Exercisable at December 31, 2019, Aggregate Intrinsic Value $ 154