Restructuring charges - Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 12,455	$ 6,508
Cost of Revenue [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	393	364
Research and Development [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,679	2,655
Sales and Marketing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,242	2,678
General and Administrative [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,141	$ 811
Non-cancelable Leases, Accelerated Depreciation and Other Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 700