Stock-Based Compensation - Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2019
Valuation Assumptions
Stock price at grant date (in dollars per share)				$ 124.00
Employee stock options
Valuation Assumptions
Expected volatility, low end of range (as a percent)	49.00%	38.60%	44.30%
Expected volatility, high end of range (as a percent)	66.50%	44.20%	47.60%
Risk-free interest rate, low end of range (as a percent)	1.60%	2.90%	1.90%
Risk-free interest rate, high end of range (as a percent)	2.50%	3.00%	2.30%
Dividend rate (as a percent)	0.00%	0.00%	0.00%
Class A common stock committed under 2016 ESPP
Valuation Assumptions
Expected term (in years)		6 months	6 months
Expected volatility, low end of range (as a percent)	43.10%	39.80%	33.20%
Expected volatility, high end of range (as a percent)	50.30%	47.50%	33.90%
Risk-free interest rate, low end of range (as a percent)	1.60%	2.10%	1.10%
Risk-free interest rate, high end of range (as a percent)	2.40%	2.50%	1.40%
Dividend rate (as a percent)	0.00%	0.00%	0.00%
Performance-based stock options
Valuation Assumptions
Asset volatility (as a percent)	40.00%
Equity volatility (as a percent)	45.00%
Discount rate (as a percent)	14.00%
Stock price at grant date (in dollars per share)	$ 31.7
Minimum | Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)	$ 103.70	$ 33.01	$ 23.60
Expected term (in years)	3 months 29 days	1 year	6 years 29 days
Minimum | Class A common stock committed under 2016 ESPP
Valuation Assumptions
Expected term (in years)	5 months 26 days
Maximum | Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)	$ 130.70	$ 76.63	$ 31.96
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days
Maximum | Class A common stock committed under 2016 ESPP
Valuation Assumptions
Expected term (in years)	6 months