Share-Based Compensation - Share-Based Payment Award Activity (Detail)	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Options
Outstanding, beginning of period | shares	1,394,888
Granted | shares	122,120
Exercised | shares	(311,575)
Forfeited | shares	(22,008)
Expired | shares	(1,520)
Outstanding, end of period | shares	1,181,905
Vested and expected to vest, end of period | shares	1,145,732
Exercisable, end of period | shares	656,191
Weighted Average Exercise Price
Outstanding, beginning of period	$ 66.03
Granted	129.30
Exercised	51.34
Forfeited	84.40
Expired	48.76
Outstanding, end of period	76.12
Vested and expected to vest, end of period	75.24
Exercisable, end of period	$ 60.34
Weighted Average Remaining Contractual Life in Years
Outstanding, end of period	4 years
Vested and expected to vest, end of period	3 years 11 months 12 days
Exercisable, end of period	3 years 4 days
Aggregate Intrinsic Value of In-The- Money Options
Outstanding, end of period | $	$ 48,295,069
Vested and expected to vest, end of period | $	47,717,566
Exercisable, end of period | $	$ 36,230,256