Share-Based Compensation - Weighted Average Assumptions and Fair Values Used for ESPP (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected term in years	4 years 7 months 6 days	4 years 9 months 18 days	4 years 10 months 24 days
Weighted average expected volatility of the Company's underlying common stock	35.50%	34.70%	33.70%
Risk-free interest rate	2.26%	2.82%	1.81%
Expected dividend yield	$ 0	$ 0	$ 0
Weighted average grant date fair value (usd per share)	$ 83.50	$ 105.81	$ 57.81
Employee Stock Purchase Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected term in years	15 days	15 days	15 days
Weighted average expected volatility of the Company's underlying common stock	38.10%	32.20%	31.20%
Risk-free interest rate	2.40%	1.79%	0.80%
Expected dividend yield	$ 0	$ 0	$ 0
Weighted average grant date fair value (usd per share)	$ 52.90	$ 62.76	$ 41.70