Stock-Based Compensation - Options Outstanding and Exercisable (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding | shares	3,682,958	[1]
Options Outstanding, Weighted-Average Remaining Contractual Life	6 years	[1]
Options Outstanding, Weighted-Average Exercise Price	$ 36.28	[1]
Options Exercisable | shares	2,575,203	[2]
Options Exercisable, Weighted-Average Exercise Price	$ 28.64	[2]
Exercise Price Range One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower limit	9.00
Range of Exercise Prices, upper limit	$ 12.99
Options Outstanding | shares	104,500	[1]
Options Outstanding, Weighted-Average Remaining Contractual Life	3 years 9 months 18 days	[1]
Options Outstanding, Weighted-Average Exercise Price	$ 12.30	[1]
Options Exercisable | shares	104,500	[2]
Options Exercisable, Weighted-Average Exercise Price	$ 12.30	[2]
Exercise Price Range Two
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower limit	13.00
Range of Exercise Prices, upper limit	$ 20.00
Options Outstanding | shares	1,250,011	[1]
Options Outstanding, Weighted-Average Remaining Contractual Life	3 years 7 months 6 days	[1]
Options Outstanding, Weighted-Average Exercise Price	$ 16.17	[1]
Options Exercisable | shares	1,250,011	[2]
Options Exercisable, Weighted-Average Exercise Price	$ 16.17	[2]
Exercise Price Range Three
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	$ 65.41
Options Outstanding | shares	2,328,447	[1]
Options Outstanding, Weighted-Average Remaining Contractual Life	7 years 4 months 24 days	[1]
Options Outstanding, Weighted-Average Exercise Price	$ 48.16	[1]
Options Exercisable | shares	1,220,692	[2]
Options Exercisable, Weighted-Average Exercise Price	$ 42.82	[2]

[1] At December 31, 2017, the aggregate intrinsic value of options outstanding was $118.4 million.

[2] At December 31, 2017, the weighted-average remaining contractual life of options exercisable was 4.9 years and the aggregate intrinsic value of options exercisable was $102.5 million.