Accounting Policies Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2018
Accounting Policies [Abstract]
Management's Use of Estimates	Management’s Use of Estimates -The preparation of the consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of income and expenses during the reporting period. Our most significant estimate is the allowance for loan losses. Other estimates include the evaluation of other-than-temporary impairment of investment securities, goodwill impairment, pension and other postretirement liabilities and an analysis of a need for a valuation allowance for deferred tax assets. Actual results could differ from those estimates. A material estimate that is particularly susceptible to significant change in the near term is the allowance for loan losses. In connection with the determination of the allowance for loan losses, management obtains appraisals for properties. The allowance for loan losses is management’s best estimate of probable loan losses incurred as of the balance sheet date. While management uses available information to recognize losses on loans, future adjustments to the allowance for loan losses may be necessary based on changes in economic conditions.
Recently Adopted and Recently Issued Accounting Standards	Recently Adopted and Recently Issued Accounting Standards The following accounting standards have been adopted in the first six months of 2018: ASU 2014-09 "Revenue from Contracts With Customers (Topic 606)" was adopted as of January 1, 2018. For additional information, see Revenue Recognition under Significant Policy Update in this Note. ASU 2016-01 "Recognition and Measurement of Financial Assets and Financial Liabilities" (Subtopic 825-10) significantly changed the income statement impact of equity investments. For Arrow, the standard became effective for the first quarter of 2018, and requires that equity investments be measured at fair value, with changes in fair value recognized in net income. The cumulative effect of the January 1, 2018 adoption was an increase to retained earnings of $331 thousand with a corresponding decrease to Accumulated Other Comprehensive Loss. For periods prior to January 1, 2018, equity securities were classified as available-for-sale and stated at fair value with unrealized gains and losses reported as a separate component of accumulated other comprehensive income, net of tax. ASU 2016-01 also emphasized the existing requirement to use exit prices to measure fair value for disclosure purposes and clarifies that entities not make use of a practicability exception in determining the fair value of loans. Accordingly, we refined the calculation used to determine the disclosed fair value of our loans as part of adopting this standard. See Note 9 to our unaudited interim consolidated financial statements entitled Fair Value of Financial Instruments. ASU 2016-15 "Statement of Cash Flows (Topic 230) - Classification of Certain Cash Receipts and Cash Payments" will reduce existing diversity in practice with respect to eight specific cash flow issues. Arrow adopted this ASU in the first quarter of 2018. ASU 2017-01 "Business Combinations" (Topic 805) defines when a set of assets and activities constitutes a business for the purposes of determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in this update allow for a business to consist of inputs, processes, and the ability to create output. For Arrow, the standard became effective in the first quarter of 2018. This update had no effect on our accounting for acquisitions and dispositions of businesses. ASU 2017-07 "Compensation-Retirement Benefits" (Topic 715) improves the presentation of net periodic pension cost and net periodic post-retirement benefit cost by requiring that an employer disaggregate the service cost component from the other components of net benefit cost. For Arrow, the standard became effective in the first quarter of 2018. In accordance with the practical expedient adoption method, for all periods presented Arrow used the amounts disclosed in the retirement plans footnote for the prior period retrospective reclassification of the non-service cost components out of salaries and benefits and into other operating expenses. The adoption of this change in accounting for pension costs did not have a material impact on our financial position or the results of operations. ASU 2017-09 "Compensation-Stock Compensation" (Topic 718) provides guidance about which changes to the terms and conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The guidance highlights the requirements for applying modification accounting and the exception criteria relating to changes in share-based payment terms. For Arrow, the standard became effective in the first quarter of 2018. The adoption of this change in accounting for share-based payment awards did not have a material impact on our financial position or the results of operations in periods subsequent to its adoption. The following accounting standards have been issued and will become effective for the Company at a future date: In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) which requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet for all leases with terms longer than 12 months. For a lease with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right-of-use asset and lease liability. Additionally, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option or not exercise an option to terminate the lease. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842. ASU 2018-01 was issued to address concerns about the cost and complexity of complying with the transition provisions of ASU 2018-01. Early adoption is permitted in any interim or annual period. For Arrow, the standard becomes effective in the first quarter of 2019. The Company is in the process of reviewing its existing lease portfolios, including service contracts for embedded leases to evaluate the impact of this standard on its consolidated financial statements and the impact on regulatory capital. The Company does not expect that this new accounting standard will have a material impact on it's financial position or the results of operations in periods subsequent to its adoption. As of June 30, 2018, there were less than $2.2 million in minimum lease payments for existing operating leases of branch and insurance locations with varying expiration dates from 2018 to 2031. In June 2016, the FASB issued ASU 2016-13 "Financial Instruments - Credit Losses" (Topic 326) which will change the way financial entities measure expected credit losses for financial assets, primarily loans. Under this ASU, the "incurred loss" model will be replaced with an "expected loss" model which will recognize losses over the life of the instrument and requires consideration of a broader range of reasonable and supportable information. Currently, credit losses on available-for-sale securities reduce the carrying value of the instrument and cannot be reversed. Under this ASU, the amount of the credit loss is carried as a valuation allowance and can be reversed. The standard also requires expanded credit quality disclosures. For Arrow, the standard is effective for the first quarter of 2020 and early adoption is allowed in 2019. The Company plans on adopting the standard in the first quarter of 2020, in order to maximize the accumulation of data needed to calculate the new CECL methodologies. The ASU describes several acceptable methodologies for calculating expected losses on a loan or a pool of loans and requires additional disclosures. The initial adjustment will not be reported in earnings, but as the cumulative effect of a change in accounting principle. The FASB’s Transition Research Group for credit losses still has several outstanding unresolved questions, some of which may have a significant impact on CECL calculations. The Company is in the process of assessing the impact of this new accounting standard as required changes to its credit loss estimation process and models are being evaluated. This will likely have the effect of reducing shareholders' equity, but the Company expects to remain a well-capitalized financial institution under current regulatory calculations. In January 2017, the FASB issued ASU 2017-04 "Intangibles-Goodwill and Other" (Topic 350) simplifies the procedures for evaluating impairment of goodwill. Prior to the adoption of this standard, entities were required to perform procedures to determine the fair value of the underlying assets and liabilities for determining the fair value of assets and liabilities in a business combination. This additional step to impairment testing has been eliminated. Under this ASU, entities will perform goodwill impairment testing by comparing the fair value of a reporting unit to its carrying value. For Arrow, the standard becomes effective in the first quarter of 2019, however, early adoption is permitted. This amendment will not affect our assessment of goodwill impairment since we currently perform the analysis of comparing carrying value to fair value of our reporting units that have goodwill and we have not had to perform a Step 2 Impairment Test to date. In March 2017, the FASB issued ASU 2017-08 "Receivables-Nonrefundable Fees and Other Costs" amends the amortization period for certain purchased callable debt securities held at a premium. This shortens the amortization period for the premium to the earliest call date. Under GAAP, entities generally amortize the premium as an adjustment of yield over the contractual life of the instrument. For Arrow, the standard becomes effective in the first quarter of 2019. We do not expect that the adoption of this change in accounting for certain callable debt securities will have a material impact on our financial position or the results of operations in periods subsequent to its adoption Significant Accounting Policy Update: Revenue Recognition - Accounting Standard Codification ("ASC") Topic 606, Revenue from Contracts with Customers, establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity's contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services promised to a customer in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services as performance obligations are satisfied. The Company adopted ASC Topic 606 as of January 1, 2018 using the modified retrospective approach, and have identified the recognition of revenue related to specific types of fiduciary activities and specific types of revenue from insurance commissions to be in the scope of this guidance. Regarding fiduciary activities, under prior GAAP, revenue was recognized from settling client estates over the time period the work was performed. With the adoption of Topic 606, revenue is recognized when the performance obligation is completed, which is when the settlement of the client estate is closed. The impact of this change in revenue recognition was not material to our consolidated financial statements. Regarding revenue from property and casualty insurance policies in which the revenue is recorded when the client elected to pay pay premiums in installments, under prior GAAP, revenue was recognized when the client premiums were billed. With the adoption of Topic 606, revenue is required to be recognized when the performance obligation is substantially completed, i.e., when the insurance policy is issued. The impact of recognizing total policy commission revenue versus our current practice of recognizing revenue when the client is billed is not material on our consolidated financial statements. The adoption of Topic 606 related to the previously described fiduciary activity and insurance commission required a cumulative effect adjustment as of January 1, 2018 to decrease retained earnings by $102 thousand. The majority of the Company's revenue-generating transactions are not subject to ASC Topic 606, including revenue generated from financial instruments, such as loans and investment securities which are presented in our consolidated income statements as components of net interest income. The following is a description of principal activities from which the Company generates its revenue from noninterest income sources that are within the scope of ASC Topic 606: Income from Fiduciary Activities: represents revenue derived mainly through the management of client investments which is based on the market value of these assets and the fee schedule contained in the applicable account management agreement. Since the revenue is mainly based on the market value of assets, this amount can be volatile as financial markets increase and decrease based on various economic factors. The terms of the account management agreements generally specify that the performance obligations are completed each quarter. Accordingly, we mainly recognize revenue from fiduciary activities on a quarterly basis. Fees for Other Services to Customers: represents general service fees for monthly deposit account maintenance and account activity plus fees from other deposit-based services. Revenue is recognized when the performance obligation is completed, which is generally on a monthly basis for account maintenance services, or upon the completion of a deposit-related transaction. Payment for such performance obligations are generally received at the time the performance obligations are satisfied. Insurance Commissions: represents commissions and fees paid by insurance carriers for both property and casualty insurance policies, and for services performed for employment benefits clients. Revenue from our property and casualty business is recognized when our performance obligation is satisfied, which is generally the effective date of the bound coverage since there are no significant performance obligations remaining. Revenue from our employment benefit brokerage business is recognized when our benefit servicing performance obligations are satisfied, generally on a monthly basis.

Recently Adopted and Recently Issued Accounting Standards

The following accounting standards have been adopted in the first six months of 2018:

ASU 2014-09 "Revenue from Contracts With Customers (Topic 606)" was adopted as of January 1, 2018. For additional information, see Revenue Recognition under Significant Policy Update in this Note.

ASU 2016-01 "Recognition and Measurement of Financial Assets and Financial Liabilities" (Subtopic 825-10) significantly changed the income statement impact of equity investments. For Arrow, the standard became effective for the first quarter of 2018, and requires that equity investments be measured at fair value, with changes in fair value recognized in net income. The cumulative effect of the January 1, 2018 adoption was an increase to retained earnings of $331 thousand with a corresponding decrease to Accumulated Other Comprehensive Loss. For periods prior to January 1, 2018, equity securities were classified as available-for-sale and stated at fair value with unrealized gains and losses reported as a separate component of accumulated other comprehensive income, net of tax. ASU 2016-01 also emphasized the existing requirement to use exit prices to measure fair value for disclosure purposes and clarifies that entities not make use of a practicability exception in determining the fair value of loans. Accordingly, we refined the calculation used to determine the disclosed fair value of our loans as part of adopting this standard. See Note 9 to our unaudited interim consolidated financial statements entitled Fair Value of Financial Instruments.

ASU 2016-15 "Statement of Cash Flows (Topic 230) - Classification of Certain Cash Receipts and Cash Payments" will reduce existing diversity in practice with respect to eight specific cash flow issues. Arrow adopted this ASU in the first quarter of 2018.

ASU 2017-01 "Business Combinations" (Topic 805) defines when a set of assets and activities constitutes a business for the purposes of determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in this update allow for a business to consist of inputs, processes, and the ability to create output. For Arrow, the standard became effective in the first quarter of 2018. This update had no effect on our accounting for acquisitions and dispositions of businesses.

ASU 2017-07 "Compensation-Retirement Benefits" (Topic 715) improves the presentation of net periodic pension cost and net periodic post-retirement benefit cost by requiring that an employer disaggregate the service cost component from the other components of net benefit cost. For Arrow, the standard became effective in the first quarter of 2018. In accordance with the practical expedient adoption method, for all periods presented Arrow used the amounts disclosed in the retirement plans footnote for the prior period retrospective reclassification of the non-service cost components out of salaries and benefits and into other operating expenses. The adoption of this change in accounting for pension costs did not have a material impact on our financial position or the results of operations.

ASU 2017-09 "Compensation-Stock Compensation" (Topic 718) provides guidance about which changes to the terms and conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The guidance highlights the requirements for applying modification accounting and the exception criteria relating to changes in share-based payment terms. For Arrow, the standard became effective in the first quarter of 2018. The adoption of this change in accounting for share-based payment awards did not have a material impact on our financial position or the results of operations in periods subsequent to its adoption.

The following accounting standards have been issued and will become effective for the Company at a future date:

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) which requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet for all leases with terms longer than 12 months. For a lease with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right-of-use asset and lease liability. Additionally, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option or not exercise an option to terminate the lease. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842. ASU 2018-01 was issued to address concerns about the cost and complexity of complying with the transition provisions of ASU 2018-01. Early adoption is permitted in any interim or annual period. For Arrow, the standard becomes effective in the first quarter of 2019. The Company is in the process of reviewing its existing lease portfolios, including service contracts for embedded leases to evaluate the impact of this standard on its consolidated financial statements and the impact on regulatory capital. The Company does not expect that this new accounting standard will have a material impact on it's financial position or the results of operations in periods subsequent to its adoption. As of June 30, 2018, there were less than $2.2 million in minimum lease payments for existing operating leases of branch and insurance locations with varying expiration dates from 2018 to 2031.

In June 2016, the FASB issued ASU 2016-13 "Financial Instruments - Credit Losses" (Topic 326) which will change the way financial entities measure expected credit losses for financial assets, primarily loans. Under this ASU, the "incurred loss" model will be replaced with an "expected loss" model which will recognize losses over the life of the instrument and requires consideration of a broader range of reasonable and supportable information. Currently, credit losses on available-for-sale securities reduce the carrying value of the instrument and cannot be reversed. Under this ASU, the amount of the credit loss is carried as a valuation allowance and can be reversed. The standard also requires expanded credit quality disclosures. For Arrow, the standard is effective for the first quarter of 2020 and early adoption is allowed in 2019. The Company plans on adopting the standard in the first quarter of 2020, in order to maximize the accumulation of data needed to calculate the new CECL methodologies. The ASU describes several acceptable methodologies for calculating expected losses on a loan or a pool of loans and requires additional disclosures. The initial adjustment will not be reported in earnings, but as the cumulative effect of a change in accounting principle. The FASB’s Transition Research Group for credit losses still has several outstanding unresolved questions, some of which may have a significant impact on CECL calculations. The Company is in the process of assessing the impact of this new accounting standard as required changes to its credit loss estimation process and models are being evaluated. This will likely have the effect of reducing shareholders' equity, but the Company expects to remain a well-capitalized financial institution under current regulatory calculations.

In January 2017, the FASB issued ASU 2017-04 "Intangibles-Goodwill and Other" (Topic 350) simplifies the procedures for evaluating impairment of goodwill. Prior to the adoption of this standard, entities were required to perform procedures to determine the fair value of the underlying assets and liabilities for determining the fair value of assets and liabilities in a business combination. This additional step to impairment testing has been eliminated. Under this ASU, entities will perform goodwill impairment testing by comparing the fair value of a reporting unit to its carrying value. For Arrow, the standard becomes effective in the first quarter of 2019, however, early adoption is permitted. This amendment will not affect our assessment of goodwill impairment since we currently perform the analysis of comparing carrying value to fair value of our reporting units that have goodwill and we have not had to perform a Step 2 Impairment Test to date.

In March 2017, the FASB issued ASU 2017-08 "Receivables-Nonrefundable Fees and Other Costs" amends the amortization period for certain purchased callable debt securities held at a premium. This shortens the amortization period for the premium to the earliest call date. Under GAAP, entities generally amortize the premium as an adjustment of yield over the contractual life of the instrument. For Arrow, the standard becomes effective in the first quarter of 2019. We do not expect that the adoption of this change in accounting for certain callable debt securities will have a material impact on our financial position or the results of operations in periods subsequent to its adoption

Significant Accounting Policy Update:

Revenue Recognition - Accounting Standard Codification ("ASC") Topic 606, Revenue from Contracts with Customers, establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity's contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services promised to a customer in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services as performance obligations are satisfied.

The Company adopted ASC Topic 606 as of January 1, 2018 using the modified retrospective approach, and have identified the recognition of revenue related to specific types of fiduciary activities and specific types of revenue from insurance commissions to be in the scope of this guidance. Regarding fiduciary activities, under prior GAAP, revenue was recognized from settling client estates over the time period the work was performed. With the adoption of Topic 606, revenue is recognized when the performance obligation is completed, which is when the settlement of the client estate is closed. The impact of this change in revenue recognition was not material to our consolidated financial statements. Regarding revenue from property and casualty insurance policies in which the revenue is recorded when the client elected to pay pay premiums in installments, under prior GAAP, revenue was recognized when the client premiums were billed. With the adoption of Topic 606, revenue is required to be recognized when the performance obligation is substantially completed, i.e., when the insurance policy is issued. The impact of recognizing total policy commission revenue versus our current practice of recognizing revenue when the client is billed is not material on our consolidated financial statements. The adoption of Topic 606 related to the previously described fiduciary activity and insurance commission required a cumulative effect adjustment as of January 1, 2018 to decrease retained earnings by $102 thousand.

The majority of the Company's revenue-generating transactions are not subject to ASC Topic 606, including revenue generated from financial instruments, such as loans and investment securities which are presented in our consolidated income statements as components of net interest income. The following is a description of principal activities from which the Company generates its revenue from noninterest income sources that are within the scope of ASC Topic 606:

Income from Fiduciary Activities: represents revenue derived mainly through the management of client investments which is based on the market value of these assets and the fee schedule contained in the applicable account management agreement. Since the revenue is mainly based on the market value of assets, this amount can be volatile as financial markets increase and decrease based on various economic factors. The terms of the account management agreements generally specify that the performance obligations are completed each quarter. Accordingly, we mainly recognize revenue from fiduciary activities on a quarterly basis.

Fees for Other Services to Customers: represents general service fees for monthly deposit account maintenance and account activity plus fees from other deposit-based services. Revenue is recognized when the performance obligation is completed, which is generally on a monthly basis for account maintenance services, or upon the completion of a deposit-related transaction. Payment for such performance obligations are generally received at the time the performance obligations are satisfied.

Insurance Commissions: represents commissions and fees paid by insurance carriers for both property and casualty insurance policies, and for services performed for employment benefits clients. Revenue from our property and casualty business is recognized when our performance obligation is satisfied, which is generally the effective date of the bound coverage since there are no significant performance obligations remaining. Revenue from our employment benefit brokerage business is recognized when our benefit servicing performance obligations are satisfied, generally on a monthly basis.