Share Based Awards - Compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 35,804	$ 38,436	$ 33,731
Cost of revenue
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	5,095	5,006	3,772
Research and development
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	14,610	15,981	14,520
Sales and marketing
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	8,663	9,464	8,659
General and administrative
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 7,436	$ 7,985	$ 6,780