SHARE-BASED COMPENSATION PLANS - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Orrstown 2011 Incentive Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved to be issued	381,920
Number of shares available to be issued under employee stock purchase plan	81,280
Orrstown 2011 Incentive Stock Plan \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 2,327	$ 2,169
Unrecognized compensation expense, recognition period	1 year 11 months 5 days
Orrstown 2011 Incentive Stock Plan \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options outstanding and exercisable	$ 116	$ 39
Orrstown 2011 Incentive Stock Plan \| Employee Stock Option \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term to exercise option	10 years
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved to be issued	350,000
Number of shares available to be issued under employee stock purchase plan	179,372
Maximum shares purchase, as percentage of salary	10.00%
Percentage of value of the shares on the semi-annual offering	95.00%

Aggregate number of common shares reserved for future issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Purchase price of common stock expressed as a percentage of its fair value.

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