INTANGIBLE ASSETS - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 213,704	$ 213,816
Accumulated Amortization	(103,698)	(96,797)
Net Carrying Amount	110,006	117,019
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	174,886	174,940
Accumulated Amortization	(69,834)	(63,727)
Net Carrying Amount	105,052	111,213
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,409	5,466
Accumulated Amortization	(5,409)	(5,306)
Net Carrying Amount	0	160
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,722	24,724
Accumulated Amortization	(21,422)	(21,146)
Net Carrying Amount	3,300	3,578
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,839	7,838
Accumulated Amortization	(6,358)	(5,976)
Net Carrying Amount	1,481	1,862
Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	848	848
Accumulated Amortization	(675)	(642)
Net Carrying Amount	$ 173	$ 206