Equity - Reclassifications Out of Accumulated Other Comprehensive (loss) Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Reclassification Adjustment Out of Accumulated Other Comprehensive (Loss) Income [Line Items]
Income (Loss) Before Income Taxes	$ 2,847	$ (9,345)
Tax benefit	(1,917)	397
Net Loss attributable to ADTRAN Holdings, Inc.	(1,321)	(11,267)
Reclassification Out of Accumulated Other Comprehensive (Loss) Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive (Loss) Income [Line Items]
Defined benefit plan adjustments - actuarial loss	(96)	190
Income (Loss) Before Income Taxes	(116)	125
Tax benefit	35	(42)
Net Loss attributable to ADTRAN Holdings, Inc.	(81)	83
Reclassification Out of Accumulated Other Comprehensive (Loss) Income [Member] | Unrealized Gain on Available-for-Sale Securities [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive (Loss) Income [Line Items]
Net realized loss on sales of securities	$ (20)	$ (65)