GOODWILL AND INTANGIBLE ASSETS, NET (Goodwill Roll Forward) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2021	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Balance beginning of period			$ 211,956	$ 195,043
Effect of net foreign currency exchange rate changes			(7,101)	3,695
Balance end of period	$ 530,723		530,723	211,956
North America
Goodwill [Roll Forward]
Balance beginning of period			121,132	113,426
Effect of net foreign currency exchange rate changes			(616)	582
Balance end of period	217,594		217,594	121,132
Europe
Goodwill [Roll Forward]
Balance beginning of period			90,106	80,873
Effect of net foreign currency exchange rate changes			(6,483)	3,160
Balance end of period	312,413		312,413	90,106
Russia
Goodwill [Roll Forward]
Balance beginning of period			718	744
Effect of net foreign currency exchange rate changes			(2)	(47)
Balance end of period	716		716	718
2020 Acquisitions
Goodwill [Roll Forward]
Purchase accounting adjustments			(24)
Acquisition				12,945
2020 Acquisitions | North America
Goodwill [Roll Forward]
Purchase accounting adjustments			0
Acquisition				6,042
2020 Acquisitions | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments			(24)
Acquisition				6,903
2020 Acquisitions | Russia
Goodwill [Roll Forward]
Purchase accounting adjustments			0
Acquisition				0
test IO
Goodwill [Roll Forward]
Purchase accounting adjustments		$ (200)		(226)
test IO | North America
Goodwill [Roll Forward]
Purchase accounting adjustments				863
test IO | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments				(1,089)
test IO | Russia
Goodwill [Roll Forward]
Purchase accounting adjustments				0
Other 2019 Acquisitions
Goodwill [Roll Forward]
Purchase accounting adjustments				499
Other 2019 Acquisitions | North America
Goodwill [Roll Forward]
Purchase accounting adjustments				219
Other 2019 Acquisitions | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments				259
Other 2019 Acquisitions | Russia
Goodwill [Roll Forward]
Purchase accounting adjustments				$ 21
Emakina
Goodwill [Roll Forward]
Acquisition			136,614
Emakina | North America
Goodwill [Roll Forward]
Acquisition			0
Emakina | Europe
Goodwill [Roll Forward]
Acquisition			136,614
Emakina | Russia
Goodwill [Roll Forward]
Acquisition			0
PolSource
Goodwill [Roll Forward]
Purchase accounting adjustments	$ 11,800
Acquisition			125,339
PolSource | North America
Goodwill [Roll Forward]
Acquisition			75,203
PolSource | Europe
Goodwill [Roll Forward]
Acquisition			50,136
PolSource | Russia
Goodwill [Roll Forward]
Acquisition			0
CORE
Goodwill [Roll Forward]
Acquisition			23,234
CORE | North America
Goodwill [Roll Forward]
Acquisition			0
CORE | Europe
Goodwill [Roll Forward]
Acquisition			23,234
CORE | Russia
Goodwill [Roll Forward]
Acquisition			0
Other 2021 Acquisitions
Goodwill [Roll Forward]
Acquisition			40,705
Other 2021 Acquisitions | North America
Goodwill [Roll Forward]
Acquisition			21,875
Other 2021 Acquisitions | Europe
Goodwill [Roll Forward]
Acquisition			18,830
Other 2021 Acquisitions | Russia
Goodwill [Roll Forward]
Acquisition			$ 0