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Share-Based Compensation - Stock Option Activity under Company's Plan - Long Term Incentive Plan (Detail) - Long Term Incentive Plan Stock Option [Member] - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding at January 1, 2018, Number of Shares 29,250  
Granted, Number of Shares 0 0
Exercised, Number of Shares 0 0
Forfeited, Number of Shares 0  
Outstanding (vested and expected to vest) at March 31, 2018, Number of Shares 29,250  
Exercisable at March 31, 2018, Number of Shares 21,625  
Outstanding at January 1, 2018, Weighted Average Exercise Price per Share $ 56.84  
Granted, Weighted Average Exercise Price per Share 0.00  
Exercised, Weighted Average Exercise Price per Share 0.00  
Forfeited, Weighted Average Exercise Price per Share 0.00  
Outstanding (vested and expected to vest) at March 31, 2018, Weighted Average Exercise Price per Share 56.84  
Exercisable at March 31, 2018, Weighted Average Exercise Price per Share $ 60.69  
Outstanding (vested and expected to vest) at March 31, 2018, Weighted Average Remaining Contractual Term 6 years 10 months 24 days  
Exercisable at March 31, 2018, Weighted Average Remaining Contractual Term 6 years 2 months 12 days  
Outstanding (vested and expected to vest) at March 31, 2018, Aggregate Intrinsic Value $ 320  
Exercisable at March 31, 2018, Aggregate Intrinsic Value $ 174