Share-Based Compensation - Stock Options Activity (Detail) - Stock Option - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Shares
Beginning balance (in shares)	2,266,433
Granted (in shares)	549,815
Exercised (in shares)	(393,142)
Forfeited/Expired (in shares)	(64,874)
Ending balance (in shares)	2,358,232	2,266,433
Vested and expected to vest (in shares)	2,204,293
Exercisable (in shares)	1,211,400
Weighted Average Price
Beginning Balance, Weighted Average Price (in dollars per share)	$ 54.05
Granted, Weighted Average Price (in dollars per share)	74.80
Exercised, Weighted Average Price (in dollars per share)	43.03
Forfeited/Expired, Weighted Average Price (in dollars per share)	71.49
Ending Balance, Weighted Average Price (in dollars per share)	$ 60.25	$ 54.05
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term	7 years 1 month 13 days	6 years 6 months 29 days
Aggregate Intrinsic Value
Stock options outstanding, Aggregate intrinsic value	$ 51,540,880	$ 51,918,028
Vested and expected to vest , Weighted Average Price (in dollars per share)	$ 59.23
Exercisable, Weighted Average Price (in dollars per share)	$ 47.70
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 11 months 23 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 6 months 7 days
Stock options, vested and expected to vest aggregate intrinsic value	$ 50,424,569
Stock options, exercisable aggregate intrinsic value	$ 41,674,285