Restructuring - Restructuring Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Charges	$ 15,491	$ 0	$ 0
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Charges	$ 16,800
2015 Restructuring
Restructuring Cost and Reserve [Line Items]
Charges		$ 300	3,500
2015 Restructuring | Cost of net revenues
Restructuring Cost and Reserve [Line Items]
Charges			2,700
2015 Restructuring | Technology and development
Restructuring Cost and Reserve [Line Items]
Charges			$ 800