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Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($)
$ in Thousands
 12 Months Ended
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 (432,263) (231,210) $ (70,963)
Tax expense (8,785) (28,133) 62,075
Net Loss attributable to ADTRAN Holdings, Inc. (450,872) (266,289) (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)