CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 270,749			$ (2,729)			$ 750,222	$ 107,210
Defined benefit pension plans:
Unrecognized actuarial gain (loss)	(1,551)			5,183			9,984	(6,406)
Applicable income taxes	413			(1,374)			(2,657)	1,724
Unrecognized gain (loss) arising during period, net of income taxes	(1,138)			3,809			7,327	(4,682)
Settlement loss (gain) included in other expense, net	(522)			122			(1,917)	895
Applicable income taxes	139			(39)			512	(246)
Settlement loss (gain) included in other expense, net, net of income taxes	(383)			83			(1,405)	649
Applicable income taxes	0			0			0	0
Foreign currency translation adjustment, net	(619)	$ (140)	$ 619	(582)	$ (517)	$ (424)	(140)	(1,523)
Other comprehensive income (loss)	(2,148)			3,310			5,774	(5,556)
Comprehensive income	268,601			581			755,996	101,654
Comprehensive income (loss) attributable to Altice USA, Inc. stockholders	264,705			(1,385)			744,423	100,155
Net loss (income) attributable to noncontrolling interests	(3,896)	$ (3,274)	$ (4,403)	(1,966)	$ (213)	$ 680	(11,573)	(1,499)
Amortization of actuarial gains	(11)			0			(11)	0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Tax	3			0			3	0
Amortization of actuarial gains included in other expense, net of tax				0			(8)	0
Foreign currency translation adjustment	$ (619)			$ (582)			$ (140)	$ (1,523)