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Fair Value Measurements - Narrative (Details) | 9 Months Ended
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Sep. 30, 2018
Fair Value Disclosures [Abstract] |
Period for order of valuations (at least) | 18 months

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- Definition Number of Minimum Months for Corporation to Order Updated Valuation + References No definition available. + Details
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Namespace Prefix: | acnb_
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Balance Type: | na
Period Type: | duration

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