CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Parent [Member]	Member's Deficiency	Accumulated Deficit	Treasury Stock	Accumulated Other Comprehensive Income	Noncontrolling Interests	Common Class A Common Stock	Common Class B Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated deficit				$ 390,766
Beginning balance at Dec. 31, 2019	$ 2,279,262	$ 2,269,964	$ 2,039,918		$ (163,904)	$ (3,250)	$ 9,298	$ 4,572	$ 1,862
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	(858)			(858)				(858)
Net income attributable to noncontrolling interests	680						680
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	9,503	9,503				9,503
Foreign currency translation adjustment, net	(424)	(424)				(424)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	27,370	27,370	27,370
Redeemable equity vested	29,479	29,479	29,479
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	13,260	13,260	13,260
Class A shares acquired through share repurchase program and retired	(749,998)	(749,998)	(749,686)					(312)
Stock Issued During Period, Value, New Issues	2,507	2,507	2,495		11			1
Ending balance at Mar. 31, 2020	1,590,415	1,581,797	1,362,836		(163,893)	(13,177)	8,618	4,261	1,862
Beginning balance at Dec. 31, 2019	2,279,262	2,269,964	2,039,918		(163,904)	(3,250)	9,298	4,572	1,862
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	105,711
Net income attributable to noncontrolling interests	(1,499)
Foreign currency translation adjustment, net	(1,523)
Ending balance at Sep. 30, 2020	745,343	734,546	405,043		(163,867)	(8,806)	10,797	3,839	1,860
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated deficit				389,908
Beginning balance at Mar. 31, 2020	1,590,415	1,581,797	1,362,836		(163,893)	(13,177)	8,618	4,261	1,862
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	111,264			111,264				111,264	0
Net income attributable to noncontrolling interests	(213)						(213)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	(1,576)	(1,576)				(1,576)
Foreign currency translation adjustment, net	(517)	(517)				(517)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	33,683	33,683	33,683
Redeemable equity vested	59,081	59,081	59,081
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	(8,764)	(8,764)	(8,764)
Class A shares acquired through share repurchase program and retired	(631,237)	(631,237)	(630,979)					(258)
Stock Issued During Period, Value, New Issues	1,965	1,965	1,939		24			2
Ending balance at Jun. 30, 2020	1,157,679	1,148,848	817,796		(163,869)	(12,118)	8,831	4,005	1,862
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated deficit				501,172
Net income (loss) attributable to Altice USA, Inc. stockholders	(4,695)			(4,695)				(4,695)	0
Net income attributable to noncontrolling interests	(1,966)						(1,966)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	(3,894)	(3,894)				(3,894)
Foreign currency translation adjustment, net	(582)	(582)				(582)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	34,057	34,057	34,057
Redeemable equity vested	5,219	5,219	5,219
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	(5,734)	(5,734)	(5,734)
Class A shares acquired through share repurchase program and retired	(448,853)	(448,853)	(448,684)					(169)
Stock Issued During Period, Value, Conversion of Convertible Securities								2	(2)
Stock Issued During Period, Value, New Issues	2,392	2,392	2,389		2			1
Ending balance at Sep. 30, 2020	745,343	734,546	405,043		(163,867)	(8,806)	10,797	3,839	1,860
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated deficit				496,477
Accumulated deficit	(985,641)
Beginning balance at Dec. 31, 2020	(1,203,139)	(1,141,030)	0	(985,641)	(163,866)	3,646	(62,109)	2,972	1,859
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	274,136	274,136		274,136
Net income attributable to noncontrolling interests	(4,403)						(4,403)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	(6,356)	(6,356)				6,356
Foreign currency translation adjustment, net	619	619				619
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	27,964	27,964		27,964
Redeemable equity vested	20,131	20,131		20,131
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	2,528	2,528		2,528
Class A shares acquired through share repurchase program and retired	(522,673)	(522,673)		(522,521)				(152)
Conversion of Class B to Class A shares								1	(1)
Stock Issued During Period, Value, New Issues	2,044	2,044		2,037	6			1
Other	58	(4,244)		(4,244)			4,302
Ending balance at Mar. 31, 2021	(1,387,573)	(1,334,169)	0	(1,185,610)	(163,860)	10,621	(53,404)	2,822	1,858
Beginning balance at Dec. 31, 2020	(1,203,139)	(1,141,030)	0	(985,641)	(163,866)	3,646	(62,109)	2,972	1,859
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	738,649
Net income attributable to noncontrolling interests	(11,573)
Foreign currency translation adjustment, net	(140)
Class A shares acquired through share repurchase program and retired	(804,928)
Ending balance at Sep. 30, 2021	(1,132,687)	(1,086,529)	0	(1,100,497)	0	9,421	(46,158)	2,689	1,858
Beginning balance at Mar. 31, 2021	(1,387,573)	(1,334,169)	0	(1,185,610)	(163,860)	10,621	(53,404)	2,822	1,858
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	197,660	197,660		197,660
Net income attributable to noncontrolling interests	(3,274)						(3,274)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	(1,088)	(1,088)				1,088
Foreign currency translation adjustment, net	(140)	(140)				(140)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	27,385	27,385		27,385
Redeemable equity vested	3,618	3,618		3,618
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	(514)	(514)		(514)
Class A shares acquired through share repurchase program and retired	(202,845)	(202,845)		(202,787)				(58)
Stock Issued During Period, Value, New Issues	8,885	8,885		(488)	9,365			8
Retirement of Treasury Stock in connection with Neptune Acquisition				(154,436)	154,495			(59)
Other	168	92		92			76
Ending balance at Jun. 30, 2021	(1,348,994)	(1,298,940)	0	(1,315,080)	0	11,569	(50,054)	2,713	1,858
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Altice USA, Inc. stockholders	266,853	266,853		266,853
Net income attributable to noncontrolling interests	(3,896)						(3,896)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Net Of Tax	1,529	1,529				(1,529)
Foreign currency translation adjustment, net	(619)	(619)				(619)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	24,172	24,172		24,172
Class A shares acquired through share repurchase program and retired	(79,410)	(79,410)		(79,384)				(26)
Stock Issued During Period, Value, New Issues	2,958	2,958		2,956				2
Other	(14)	(14)		(14)
Ending balance at Sep. 30, 2021	(1,132,687)	$ (1,086,529)	$ 0	$ (1,100,497)	$ 0	$ 9,421	$ (46,158)	$ 2,689	$ 1,858
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated deficit	$ (1,100,497)