INTANGIBLE ASSETS - Schedule of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Identifiable intangible assets [Abstract]
Gross carrying amount	$ 329,063	$ 330,063
Accumulated amortization	220,810	208,403
Customer relationships & lists
Identifiable intangible assets [Abstract]
Gross carrying amount	242,089	243,557
Accumulated amortization	$ 165,886	158,051
Customer relationships & lists | Minimum
Identifiable intangible assets [Abstract]
Amortization period	10 years
Customer relationships & lists | Maximum
Identifiable intangible assets [Abstract]
Amortization period	20 years
Trademarks & trade names
Identifiable intangible assets [Abstract]
Gross carrying amount	$ 43,169	43,208
Accumulated amortization	$ 27,112	24,974
Trademarks & trade names | Minimum
Identifiable intangible assets [Abstract]
Amortization period	2 years
Trademarks & trade names | Maximum
Identifiable intangible assets [Abstract]
Amortization period	17 years
Developed technology
Identifiable intangible assets [Abstract]
Gross carrying amount	$ 20,351	20,437
Accumulated amortization	$ 14,210	13,693
Developed technology | Minimum
Identifiable intangible assets [Abstract]
Amortization period	5 years
Developed technology | Maximum
Identifiable intangible assets [Abstract]
Amortization period	12 years
Other
Identifiable intangible assets [Abstract]
Gross carrying amount	$ 23,454	22,861
Accumulated amortization	$ 13,602	$ 11,685
Other | Minimum
Identifiable intangible assets [Abstract]
Amortization period	2 years
Other | Maximum
Identifiable intangible assets [Abstract]
Amortization period	18 years