Restructuring (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred		$ 49,300		$ 12,700		$ 62,000
Restructuring Reserve [Roll Forward]
Balance as of January 1, 2018				14,243
Costs incurred	$ (732)		$ 332	14,442	$ 3,303
Cash disbursements				(23,394)
Software and other non-cash charges				(4,605)
Translation adjustments and other				501
Balance as of September 30, 2018	1,187	14,243		1,187		1,187
Employee Severance and Related Benefits
Restructuring Reserve [Roll Forward]
Balance as of January 1, 2018				12,857
Costs incurred				5,910
Cash disbursements				(18,509)
Software and other non-cash charges				0
Translation adjustments and other				706
Balance as of September 30, 2018	964	12,857		964		964
Software Charges
Restructuring Reserve [Roll Forward]
Balance as of January 1, 2018				0
Costs incurred				2,818
Cash disbursements				0
Software and other non-cash charges				(2,818)
Translation adjustments and other				0
Balance as of September 30, 2018	0	0		0		0
Excess Facilities, Contract Terminations and Other
Restructuring Reserve [Roll Forward]
Balance as of January 1, 2018				1,386
Costs incurred				5,714
Cash disbursements				(4,885)
Software and other non-cash charges				(1,787)
Translation adjustments and other				(205)
Balance as of September 30, 2018	$ 223	$ 1,386		$ 223		$ 223