Employee benefit plans - Allocation of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense, before income taxes	$ 80,680	$ 71,399	$ 10,887
Total tax benefit recognized	(27,971)	(19,471)	(1,104)
Total stock-based compensation expense, net of income taxes	52,709	51,928	9,783
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense, before income taxes	1,492	835	690
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense, before income taxes	18,024	11,640	3,003
Selling and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense, before income taxes	13,762	10,428	5,670
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense, before income taxes	$ 47,402	$ 48,496	$ 1,524