Share-Based Compensation - Share-Based Payment Award Activity (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Options
Outstanding, beginning of period, in shares | shares	679,659
Granted, in shares | shares	1,328
Exercised, in shares | shares	(44,973)
Forfeited, in shares | shares	(1,897)
Outstanding, end of period, in shares | shares	634,117
Vested and expected to vest, end of period, in shares | shares	620,349
Exercisable, end of period, in shares | shares	366,474
Weighted Average Exercise Price
Outstanding, beginning of period, in usd per share | $ / shares	$ 137.19
Granted, in usd per share | $ / shares	239.56
Exercised, in usd per share | $ / shares	73.17
Forfeited, in usd per share | $ / shares	168.90
Outstanding, end of period, in usd per share | $ / shares	141.85
Vested and expected to vest, end of period, in usd per share | $ / shares	139.89
Exercisable, end of period, in usd per share | $ / shares	$ 103.35
Weighted Average Remaining Contractual Life - in Years
Outstanding, end of period	3 years 5 months 13 days
Vested and expected to vest, end of period	3 years 4 months 28 days
Exercisable, end of period	2 years 4 months 10 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period | $	$ 58,330,402
Vested and expected to vest, end of period | $	57,863,381
Exercisable, end of period | $	$ 43,630,770