Share-Based Compensation - Stock Options Activity (Detail) - Stock Option - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Shares
Beginning balance (in shares)	2,266,433
Granted (in shares)	558,420
Exercised (in shares)	(526,918)
Forfeited/Expired (in shares)	(162,969)
Ending balance (in shares)	2,134,966	2,266,433
Vested and expected to vest (in shares)	2,013,213
Exercisable (in shares)	1,092,881
Weighted Average Price
Beginning Balance, Weighted Average Price (in dollars per share)	$ 54.05
Granted, Weighted Average Price (in dollars per share)	75.01
Exercised, Weighted Average Price (in dollars per share)	43.52
Forfeited, Weighted Average Price (in dollars per share)	72.69
Ending Balance, Weighted Average Price (in dollars per share)	$ 60.71	$ 54.05
Weighted-Average Remaining Contractual Term
Stock options outstanding, Weighted-Average Remaining Contractual Term	6 years 11 months 12 days	6 years 6 months 29 days
Aggregate Intrinsic Value
Stock options outstanding, Aggregate intrinsic value	$ 70,154,123	$ 51,918,028
Vested and expected to vest , Weighted Average Price (in dollars per share)	$ 59.83
Exercisable, Weighted Average Price (in dollars per share)	$ 48.34
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 10 months 2 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 4 months 24 days
Aggregate Intrinsic Value, Vested and expected to vest	$ 67,927,238
Aggregate Intrinsic Value, Exercisable	$ 49,426,856