Share-Based Compensation - Share-Based Payment Award Activity (Detail)	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Options
Outstanding, beginning of period, in shares | shares	1,010,557.000
Exercised, in shares | shares	(232,370)
Granted, in shares | shares	113,535
Forfeited, in shares | shares	(9,491)
Outstanding, end of period, in shares | shares	882,231
Vested and expected to vest, end of period, in shares | shares	857,176
Exercisable, end of period, in shares | shares	533,847
Weighted Average Exercise Price
Outstanding, beginning of period, in usd per share | $ / shares	$ 87.24
Granted, in usd per share | $ / shares	178.23
Exercised, in usd per share | $ / shares	70.79
Forfeited, in usd per share | $ / shares	111.48
Outstanding, end of period, in usd per share | $ / shares	103.02
Vested and expected to vest, end of period, in usd per share | $ / shares	101.94
Exercisable, end of period, in usd per share | $ / shares	$ 83.46
Weighted Average Remaining Contractual Life - in Years
Outstanding, end of period	3 years 9 months 19 days
Vested and expected to vest, end of period	3 years 8 months 28 days
Exercisable, end of period	2 years 8 months 24 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period | $	$ 74,172,891
Vested and expected to vest, end of period | $	72,987,562
Exercisable, end of period | $	$ 55,323,524