Share Based Awards - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 8,012	$ 9,380	$ 27,159	$ 28,493
Cost of revenue
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	1,052	1,223	3,859	3,672
Research and development
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	3,279	3,670	11,015	11,780
Sales and marketing
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	2,029	2,653	6,367	7,341
General and administrative
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 1,652	$ 1,834	$ 5,918	$ 5,700