INTANGIBLE ASSETS - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 213,491	$ 213,778
Accumulated Amortization	(92,993)	(82,406)
Net Carrying Amount	120,498	131,372
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	174,727	174,894
Accumulated Amortization	(60,440)	(51,160)
Net Carrying Amount	114,287	123,734
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,414	5,433
Accumulated Amortization	(5,174)	(4,882)
Net Carrying Amount	240	551
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,679	24,753
Accumulated Amortization	(20,983)	(20,594)
Net Carrying Amount	3,696	4,159
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,827	7,847
Accumulated Amortization	(5,775)	(5,187)
Net Carrying Amount	2,052	2,660
Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	844	851
Accumulated Amortization	(621)	(583)
Net Carrying Amount	$ 223	$ 268