INTANGIBLE ASSETS - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 213,761	$ 213,778
Accumulated Amortization	(86,060)	(82,406)
Net Carrying Amount	127,701	131,372
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	174,909	174,894
Accumulated Amortization	(54,317)	(51,160)
Net Carrying Amount	120,592	123,734
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,443	5,433
Accumulated Amortization	(5,015)	(4,882)
Net Carrying Amount	428	551
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,723	24,753
Accumulated Amortization	(20,725)	(20,594)
Net Carrying Amount	3,998	4,159
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,838	7,847
Accumulated Amortization	(5,405)	(5,187)
Net Carrying Amount	2,433	2,660
Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	848	851
Accumulated Amortization	(598)	(583)
Net Carrying Amount	$ 250	$ 268