Share-Based Compensation - Stock Options Activity (Details) - Stock Option - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Shares
Beginning balance (in shares)	1,987,946
Granted (in shares)	437,500
Exercised (in shares)	(231,932)
Forfeited/Expired (in shares)	(37,642)
Ending balance (in shares)	2,155,872	1,987,946
Vested and expected to vest (in shares)	2,012,365
Exercisable (in shares)	1,078,817
Weighted Average Price
Beginning Balance, Weighted Average Price (in dollars per share)	$ 61.83
Granted, Weighted Average Price (in dollars per share)	93.22
Exercised, Weighted Average Price (in dollars per share)	55.98
Forfeited, Weighted Average Price (in dollars per share)	77.76
Ending Balance, Weighted Average Price (in dollars per share)	$ 68.56	$ 61.83
Weighted-Average Remaining Contractual Term
Stock options outstanding, Weighted-Average Remaining Contractual Term	7 years 29 days	6 years 10 months 2 days
Aggregate Intrinsic Value
Stock options outstanding, Aggregate intrinsic value	$ 95,835,269	$ 56,144,876
Vested and expected to vest , Weighted Average Price (in dollars per share)	$ 67.41
Exercisable, Weighted Average Price (in dollars per share)	$ 54.24
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 11 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 5 months 5 days
Aggregate Intrinsic Value, Vested and expected to vest	$ 91,759,774
Aggregate Intrinsic Value, Exercisable	$ 63,406,719