GOODWILL AND OTHER INTANGIBLE ASSETS, Finite-lived Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 163,149	$ 164,858
Accumulated amortization	(84,624)	(70,027)
Carrying amount, net	78,525	94,831	$ 112,297
Amortization expense	17,266	18,061	$ 20,621
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	162,200	163,022
Accumulated amortization	(83,806)	(68,446)
Carrying amount, net	78,394	94,576
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	949	1,836
Accumulated amortization	(818)	(1,581)
Carrying amount, net	$ 131	$ 255