Percent of post transaction outstanding shares of the acquiring entity issued or issuable to acquire entity.

No definition available.

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Namespace Prefix:	acnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Business Combination, Acquired Receivables, Credit Fair Value Adjustments

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business Combination, Acquired Receivables, Interest Rate Fair Value Adjustments

+ References

No definition available.

+ Details

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- Definition

Amount of deposits acquired at the acquisition date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Number of full-service retail bank offices acquired.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

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Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Name:	us-gaap_BusinessAcquisitionLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionSharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
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- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 30
-Section 30
-Paragraph 7
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- Definition

Costs incurred to effect a business combination which have been expensed during the period. Such costs could include business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Amount of assets acquired at the acquisition date.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
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Balance Type:	debit
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- Definition

Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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-Paragraph 1
-Subparagraph (c)
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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
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-Paragraph 1
-Subparagraph (a)
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- Definition

Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

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- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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-Name Accounting Standards Codification
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Acquisition of New Windsor Bancorp, Inc. - Narrative (Details)		3 Months Ended		9 Months Ended
	Jul. 01, 2017 USD ($) bank $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) bank	Sep. 30, 2016 USD ($)	Jun. 30, 2017 $ / shares	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of retail banking office locations, NWSB \| bank				7
Goodwill		$ 19,580,000	$ 6,308,000	$ 19,580,000	$ 6,308,000		$ 6,308,000
Merger related expenses		4,305,000	$ 0	$ 4,675,000	$ 0
Core deposit intangibles
Business Acquisition [Line Items]
Amortization period				10 years
New Windsor
Business Acquisition [Line Items]
Number of retail banking office locations, NWSB \| bank	7
Fair Value of total assets acquired	$ 319,821,000
Fair value of total loans acquired	263,450,000
Fair value of total deposits acquired	293,300,000
Goodwill	13,272,000	$ 13,272,000		$ 13,272,000
Cash portion of purchase price	$ 4,519,995
Percent of post transaction outstanding shares of the Corporation's common stock issued in merger	13.00%
Total consideration paid	$ 33,289,975
ACNB’s share price for purposes of calculation (in dollars per share) \| $ / shares	$ 30.50					$ 30.50
Loans receivable, gross amortized cost basis	$ 272,646,000
Interest rate fair value discount	731,000
Credit fair value discount	4,501,000
New Windsor \| Long-term Borrowings
Business Acquisition [Line Items]
Liabilities, fair value discount	$ 312,500
New Windsor \| Core deposit intangibles
Business Acquisition [Line Items]
Amortization period	10 years			10 years
New Windsor \| Investment Securities Available-for-sale
Business Acquisition [Line Items]
Assets, fair value premium (discount)	$ 361,000
New Windsor \| Time Deposits
Business Acquisition [Line Items]
Assets, fair value premium (discount)	$ (847,500)
New Windsor \| Common Stock
Business Acquisition [Line Items]
Shares of common stock issued in merger (in shares) \| shares	938,360