GOODWILL - Roll Forward (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Goodwill [Roll Forward]
Balance as of January 1, 2017	$ 109,289
Effect of net foreign currency exchange rate changes	1,002
Balance as of March 31, 2017	110,291
North America
Goodwill [Roll Forward]
Balance as of January 1, 2017	76,812
Effect of net foreign currency exchange rate changes	144
Balance as of March 31, 2017	76,604
Europe
Goodwill [Roll Forward]
Balance as of January 1, 2017	32,477
Effect of net foreign currency exchange rate changes	858
Balance as of March 31, 2017	33,687
Other Acquisitions
Goodwill [Roll Forward]
Purchase accounting adjustments	0
Other Acquisitions | North America
Goodwill [Roll Forward]
Purchase accounting adjustments	(352)
Other Acquisitions | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments	$ 352