CHANGE IN ACCOUNTING POLICIES AND ATS ACQUISITION - Narrative (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue		$ 182,034	$ 190,056
Contract assets		30,758	26,405
Goodwill		8,142,309	8,012,416		$ 8,019,861
Altice Technical Services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill				$ (23,101)
Restatement Adjustment | Impact of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue	$ 6,978
Cumulative effect on retained earnings, net of tax	17,759
Cumulative effect on retained earnings, tax	6,570
Contract assets	24,329
Restatement Adjustment | Installation Services | Impact of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	5,093
Cumulative effect on retained earnings, tax	$ 1,885
Restatement Adjustment | Altice Technical Services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill			(23,101)
CSC Holdings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		$ 8,142,309	$ 8,012,416