Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017 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	$ 30
Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	4 years
Unrecognized compensation expense | $	$ 8.0
Weighted average period to recognize expense	1 year 4 months 24 days
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Other than options, Shares granted | shares	1.0
Other than options, weighted average grant date fair value | $ / shares	$ 113.39
Vesting period (in years)	4 years
Unrecognized compensation expense | $	$ 150.1
Weighted average period to recognize expense	1 year 7 months 6 days
Performance Based Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Other than options, Shares granted | shares	0.2
Other than options, weighted average grant date fair value | $ / shares	$ 109.36
Vesting period (in years)	3 years
Unrecognized compensation expense | $	$ 27.7
Weighted average period to recognize expense	1 year 1 month 6 days