Share-Based Compensation - Stock Option Information Related to Equity Incentive Plan (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Options
Outstanding, beginning of period (in shares) | shares	808,049
Granted (in shares) | shares	90,375
Exercised (in shares) | shares	(199,659)
Forfeited (in shares) | shares	(16,769)
Expired (in shares) | shares	(2,337)
Outstanding, end of period (in shares) | shares	679,659
Vested and expected to vest (in shares) | shares	662,702
Exercisable (in shares) | shares	410,897
Weighted average exercise price
Outstanding, beginning of period (usd per share) | $ / shares	$ 105.68
Granted (usd per share) | $ / shares	305.19
Exercised (usd per share) | $ / shares	83.74
Forfeited (usd per share) | $ / shares	171.07
Expired (usd per share) | $ / shares	60.37
Outstanding, end of period (usd per share) | $ / shares	137.19
Vested and expected to vest (usd per share) | $ / shares	135.01
Exercisable (usd per share) | $ / shares	$ 100.03
Weighted Average Remaining Contractual Life in Years
Outstanding (in years)	3 years 6 months 5 days
Vested and expected to vest (in years)	3 years 5 months 17 days
Exercisable (in years)	2 years 5 months 2 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding | $	$ 46,038,508
Vested and expected to vest | $	45,667,197
Exercisable | $	$ 36,986,923