Share-Based Compensation - Share-Based Payment Award Activity (Detail)	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Options
Outstanding, beginning of period, in shares | shares	1,010,557.000
Exercised, in shares | shares	(196,006)
Granted, in shares | shares	111,855
Forfeited, in shares | shares	(3,662)
Outstanding, end of period, in shares | shares	922,744
Vested and expected to vest, end of period, in shares | shares	893,276
Exercisable, end of period, in shares | shares	568,202
Weighted Average Exercise Price
Outstanding, beginning of period, in usd per share | $ / shares	$ 87.24
Exercised, in usd per share | $ / shares	69.93
Granted, in usd per share | $ / shares	178.16
Forfeited, in usd per share | $ / shares	93.88
Outstanding, end of period, in usd per share | $ / shares	101.91
Vested and expected to vest, end of period, in usd per share | $ / shares	100.71
Exercisable, end of period, in usd per share | $ / shares	$ 82.89
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 9 days
Exercisable, end of period	2 years 11 months 12 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period | $	$ 68,457,617
Vested and expected to vest, end of period | $	67,315,191
Exercisable, end of period | $	$ 52,783,813