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Employee Benefit Plans (Retiree Medical Coverage) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Maximum number of years medical, dental and prescription drug coverage to spouses of retired former officers	30 years
Total liability recorded to provide medical, dental and prescription drug coverage	$ 0.2	$ 0.1

X

- Definition

The maximum number of years medical, dental and prescription coverage is extended to the spouse of a former officer.

+ References

No definition available.

+ Details

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Namespace Prefix:	adtn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant