Share-Based Compensation - Share-Based Payment Award Activity (Details)	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Options
Outstanding, beginning of period, in shares | shares	679,659
Granted, in shares | shares	119,835
Exercised, in shares | shares	(88,600)
Forfeited, in shares | shares	(16,265)
Expired, in shares | shares	(720)
Outstanding, end of period, in shares | shares	693,909
Vested and expected to vest, end of period, in shares | shares	673,285
Exercisable, end of period, in shares | shares	427,405
Weighted Average Exercise Price
Outstanding, beginning of period, in usd per share | $ / shares	$ 137.19
Granted, in usd per share | $ / shares	250.31
Exercised, in usd per share | $ / shares	80.99
Forfeited, in usd per share | $ / shares	208.27
Expired, in usd per share | $ / shares	64.37
Outstanding, end of period, in usd per share | $ / shares	162.31
Vested and expected to vest, end of period, in usd per share | $ / shares	159.83
Exercisable, end of period, in usd per share | $ / shares	$ 120.15
Weighted Average Remaining Contractual Life - in Years
Outstanding, end of period	3 years 10 months 28 days
Vested and expected to vest, end of period	3 years 10 months 2 days
Exercisable, end of period	2 years 8 months 15 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period | $	$ 52,916,546
Vested and expected to vest, end of period | $	52,600,866
Exercisable, end of period | $	$ 46,281,877