Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2024	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments - actuarial (loss) gain							$ 860	$ 1,791
Loss Before Income Taxes	$ (20,243)	$ (30,576)	$ (45,026)	$ (346,882)	$ (391,908)	$ (422,484)	(442,727)	(233,607)	$ (70,963)
Tax expense	(23,461)	(390)	(2,136)	18,647	16,511	16,121	(7,340)	(28,299)	62,075
Net Loss attributable to ADTRAN Holdings, Inc.	$ (46,111)	$ (33,348)	$ (49,667)	$ (330,765)	$ (380,432)	$ (413,780)	(459,891)	(268,852)	(2,037)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments - actuarial (loss) gain							(233)	145	113
Loss Before Income Taxes							(17)	(233)	(215)
Tax expense							16	53	50
Net Loss attributable to ADTRAN Holdings, Inc.							(1)	(180)	(165)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Gains (Loss) on Available-for-Sale Securities [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized gain (loss) on sales of securities							$ 216	$ (378)	$ (328)