INTANGIBLE ASSETS - Summary of Acquired Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7,149,688	$ 7,075,611
Accumulated Amortization	(3,284,685)	(2,882,787)
Net Carrying Amount	3,865,003	4,192,824
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,017,994	5,970,884
Accumulated Amortization	(2,512,269)	(2,162,110)
Net Carrying Amount	3,505,725	3,808,774
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,081,083	1,067,083
Accumulated Amortization	(749,615)	(701,998)
Net Carrying Amount	331,468	365,085
Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	50,611	37,644
Accumulated Amortization	(22,801)	(18,679)
Net Carrying Amount	$ 27,810	$ 18,965
Minimum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	8 years
Minimum | Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	2 years
Minimum | Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	1 year
Maximum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	18 years
Maximum | Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	5 years
Maximum | Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible useful life	15 years