Share-Based Compensation - Weighted Average Assumptions and Fair Values Used for ESPP (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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 7 months 6 days	4 years 9 months 18 days
Weighted average expected volatility of the Company's underlying common stock	41.90%	35.50%	34.70%
Risk-free interest rate	0.37%	2.26%	2.82%
Expected dividend yield	$ 0	$ 0	$ 0
Weighted average grant date fair value (usd per share)	$ 66.44	$ 83.50	$ 105.81
Employee Stock Purchase Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected term in years	6 months	6 months	6 months
Weighted average expected volatility of the Company's underlying common stock	51.90%	38.10%	32.20%
Risk-free interest rate	1.12%	2.40%	1.79%
Expected dividend yield	$ 0	$ 0	$ 0
Weighted average grant date fair value (usd per share)	$ 69.54	$ 52.90	$ 62.76