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Stock Based Compensation - Outstanding Stock Options Granted In Relation to Option Price and Weighted Average Maturity (Detail)
12 Months Ended
Dec. 31, 2018
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding | shares 52,500
Weighted Average Price $ 21.55
Weighted Average Life Remaining 1 year 11 months
Exercise Price 1 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, Lower Limit $ 15.01
Range of Exercise Prices, Upper Limit $ 20.00
Options Outstanding | shares 13,500
Weighted Average Price $ 18.76
Weighted Average Life Remaining 3 years 4 months
Exercise Price 2 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, Lower Limit $ 20.01
Range of Exercise Prices, Upper Limit $ 22.50
Options Outstanding | shares 25,500
Weighted Average Price $ 20.83
Weighted Average Life Remaining 1 year 5 months
Exercise Price 3 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, Lower Limit $ 22.51
Options Outstanding | shares 13,500
Weighted Average Price $ 25.72
Weighted Average Life Remaining 1 year 4 months