Annual report pursuant to Section 13 and 15(d)

Stock Based Compensation - Stock Options Outstanding (Detail)

v3.8.0.1
Stock Based Compensation - Stock Options Outstanding (Detail)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Outstanding, Options | shares 94,606
Outstanding, Weighted average exercise price $ 52.24
Exercisable, Options | shares 93,106
Exercisable, Weighted average exercise price $ 51.85
Intrinsic value of outstanding stock options at December 31, 2017 | $ $ 3,512,314
Intrinsic value of exercisable stock options at December 31, 2017 | $ $ 3,492,589
$30.00 - 39.99 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, minimum $ 30.00
Exercise Price Range, maximum $ 39.99
Outstanding, Options | shares 500
Outstanding, Weighted average exercise price $ 35.73
Exercisable, Options | shares 500
Exercisable, Weighted average exercise price $ 35.73
$40.00 - 69.99 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, minimum 40.00
Exercise Price Range, maximum $ 69.99
Outstanding, Options | shares 76,606
Outstanding, Weighted average exercise price $ 44.68
Exercisable, Options | shares 76,606
Exercisable, Weighted average exercise price $ 44.68
$70.00 - 91.58 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, minimum 70.00
Exercise Price Range, maximum $ 91.58
Outstanding, Options | shares 17,500
Outstanding, Weighted average exercise price $ 85.78
Exercisable, Options | shares 16,000
Exercisable, Weighted average exercise price $ 86.71