Summary of Options (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
NUMBER OF SHARES
Options outstanding, beginning balance | shares	4,466,900
Granted | shares	605,300
Exercised | shares	(895,100)
Cancelled | shares	(120,900)
Options outstanding, ending balance | shares	4,056,200
Vested and expected to vest, end of period | shares	3,949,100
Exercisable, end of period | shares	2,295,200
PER SHARE EXERCISE PRICE
Options outstanding, beginning balance | $ / shares	$ 48.15	[1]
Granted | $ / shares	67.63	[1]
Exercised | $ / shares	44.74	[1]
Cancelled | $ / shares	56.28	[1]
Options outstanding, ending balance | $ / shares	51.57	[1]
Vested and expected to vest, end of period | $ / shares	51.31	[1]
Exercisable, end of period | $ / shares	$ 45.79	[1]
REMAINING CONTRACTUAL LIFE IN YEARS
Options outstanding, ending balance	5 years 8 months 23 days	[1]
Vested and expected to vest, end of period	5 years 7 months 24 days	[1]
Exercisable, end of period	3 years 10 months 3 days	[1]
AGGREGATE INTRINSIC VALUE
Options outstanding, ending balance | $	$ 79.1
Vested and expected to vest, end of period | $	78.1
Exercisable, end of period | $	$ 58.0

[1] Weighted Average