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Stockholders' Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based Compensation Expense
Stock-based compensation expense		$ 42,065	$ 28,484	$ 15,343
Stock options outstanding
Stock-based Compensation Expense
Unrecognized stock-based compensation expense		$ 13,409
Weighted-average amortization period		2 years 8 months 12 days
Restricted stock units outstanding
Stock-based Compensation Expense
Unrecognized stock-based compensation expense		$ 91,395
Weighted-average amortization period		2 years 10 months 24 days
ESPP
Stock-based Compensation Expense
Unrecognized stock-based compensation expense		$ 1,455
Weighted-average amortization period		4 months 24 days
Cost of revenue
Stock-based Compensation Expense
Stock-based compensation expense		$ 6,334	3,333	2,202
Research and development
Stock-based Compensation Expense
Stock-based compensation expense		7,658	5,303	3,042
Sales and marketing
Stock-based Compensation Expense
Stock-based compensation expense		11,368	6,307	4,364
General and administrative
Stock-based Compensation Expense
Stock-based compensation expense		$ 16,705	$ 13,541	$ 5,735
Board of Directors Executive Chairman \| General and administrative
Stock-based Compensation Expense
Stock-based compensation expense	$ 1,000