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Employee Benefit Plans (Pension Benefit Plan) - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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Compensation And Retirement Disclosure [Abstract] |  |
Net actuarial loss | $ (12,973) | $ (11,256)

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- Definition Defined benefit plan accumulated other comprehensive income net actuarial gains losses net of tax. + References No definition available. + Details
Name: | adtn_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetActuarialGainsLossesNetOfTax
Namespace Prefix: | adtn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration