GOODWILL AND OTHER INTANGIBLE ASSETS - Finite-lived Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 169,039	$ 163,149
Accumulated Amortization	(101,832)	(84,624)
Carrying Amount, net	67,207	78,525	$ 94,831
Amortization expense	16,586	17,266	$ 18,061
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	168,255	162,200
Accumulated Amortization	(101,200)	(83,806)
Carrying Amount, net	67,055	78,394
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	784	949
Accumulated Amortization	(632)	(818)
Carrying Amount, net	$ 152	$ 131