Share-Based Compensation - Schedule of Stock Options Outstanding and Exercisable (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Shares | shares	2,258,000
Options Exercisable, Shares | shares	1,683,000
$26.68-$33.95
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price Range, minimum (in dollars per share)	$ 26.68
Exercise Price Range, maximum (in dollars per share)	$ 33.95
Options Outstanding, Shares | shares	454,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 31.60
Options Outstanding, Weighted Average Remaining Contractual Term (in Years)	5 years 4 months 13 days
Options Exercisable, Shares | shares	257,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 31.93
$34.33-$36.87
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price Range, minimum (in dollars per share)	34.33
Exercise Price Range, maximum (in dollars per share)	$ 36.87
Options Outstanding, Shares | shares	526,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 35.66
Options Outstanding, Weighted Average Remaining Contractual Term (in Years)	6 years 7 days
Options Exercisable, Shares | shares	364,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 35.84
$36.89-$39.84
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price Range, minimum (in dollars per share)	36.89
Exercise Price Range, maximum (in dollars per share)	$ 39.84
Options Outstanding, Shares | shares	453,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 38.01
Options Outstanding, Weighted Average Remaining Contractual Term (in Years)	3 years 6 months 14 days
Options Exercisable, Shares | shares	409,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 38.10
$40.36-$47.46
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price Range, minimum (in dollars per share)	40.36
Exercise Price Range, maximum (in dollars per share)	$ 47.46
Options Outstanding, Shares | shares	465,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 42.66
Options Outstanding, Weighted Average Remaining Contractual Term (in Years)	5 years
Options Exercisable, Shares | shares	293,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 43.70
$50.62-$70.55
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price Range, minimum (in dollars per share)	50.62
Exercise Price Range, maximum (in dollars per share)	$ 70.55
Options Outstanding, Shares | shares	360,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 59.95
Options Outstanding, Weighted Average Remaining Contractual Term (in Years)	9 months 11 days
Options Exercisable, Shares | shares	360,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 59.95