INTANGIBLE ASSETS - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 213,838	$ 213,778
Accumulated Amortization	(89,713)	(82,406)
Net Carrying Amount	124,125	131,372
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	174,933	174,894
Accumulated Amortization	(57,466)	(51,160)
Net Carrying Amount	117,467	123,734
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,469	5,433
Accumulated Amortization	(5,163)	(4,882)
Net Carrying Amount	306	551
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,742	24,753
Accumulated Amortization	(20,871)	(20,594)
Net Carrying Amount	3,871	4,159
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,844	7,847
Accumulated Amortization	(5,601)	(5,187)
Net Carrying Amount	2,243	2,660
Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	850	851
Accumulated Amortization	(612)	(583)
Net Carrying Amount	$ 238	$ 268