INTANGIBLE ASSETS - Summary of Acquired Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7,152,025	$ 7,151,788
Accumulated Amortization	(4,054,809)	(3,670,679)
Net Carrying Amount	3,097,216	3,481,109
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,017,524	6,017,524
Accumulated Amortization	(3,174,454)	(2,843,561)
Net Carrying Amount	2,843,070	3,173,963
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,081,083	1,081,083
Accumulated Amortization	(846,929)	(798,484)
Net Carrying Amount	234,154	282,599
Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	53,418	53,181
Accumulated Amortization	(33,426)	(28,634)
Net Carrying Amount	$ 19,992	$ 24,547
Minimum | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	8 years
Minimum | Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	2 years
Minimum | Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	1 year
Maximum | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	18 years
Maximum | Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	5 years
Maximum | Other amortizable intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	15 years