GOODWILL - Roll Forward (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
Balance as of January 1, 2017	$ 109,289
Effect of net foreign currency exchange rate changes	1,998
Balance as of June 30, 2017	116,239
North America
Goodwill [Roll Forward]
Balance as of January 1, 2017	76,812
Effect of net foreign currency exchange rate changes	332
Balance as of June 30, 2017	77,058
Europe
Goodwill [Roll Forward]
Balance as of January 1, 2017	32,477
Effect of net foreign currency exchange rate changes	1,666
Balance as of June 30, 2017	39,181
Other Acquisitions
Goodwill [Line Items]
Goodwill, Acquired During Period	4,732
Goodwill [Roll Forward]
Purchase accounting adjustments	220
Other Acquisitions | North America
Goodwill [Line Items]
Goodwill, Acquired During Period	199
Goodwill [Roll Forward]
Purchase accounting adjustments	(285)
Other Acquisitions | Europe
Goodwill [Line Items]
Goodwill, Acquired During Period	4,533
Goodwill [Roll Forward]
Purchase accounting adjustments	$ 505