Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee stock options, granted | shares	0.2
Employee stock options, weighted average grant date fair value | $ / shares	$ 45.87
Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Other than options, award vesting period (in years)	1 year 4 months 26 days
Unrecognized compensation expense | $	$ 11.7
Weighted average period to recognize expense	4 years
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Other than options, Shares granted | shares	0.7
Other than options, weighted average grant date fair value | $ / shares	$ 167.5
Other than options, award vesting period (in years)	1 year 9 months 24 days
Unrecognized compensation expense | $	$ 220.1
Weighted average period to recognize expense	4 years
Performance Based Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Other than options, Shares granted | shares	0.1
Other than options, weighted average grant date fair value | $ / shares	$ 162.42
Other than options, award vesting period (in years)	1 year 1 month
Unrecognized compensation expense | $	$ 43.1
Weighted average period to recognize expense	3 years