Share Based Awards - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 10,693	$ 6,547
Cost of revenue
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	1,382	701
Research and development
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	4,767	2,766
Sales and marketing
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	2,529	1,772
General and administrative
Allocation of employee service stock-based compensation expense
Stock-based compensation expense	$ 2,015	$ 1,308