Accounting Policies, by Policy (Policies)	6 Months Ended
Jun. 30, 2015
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation: The unaudited financial statements for the six months ended June 30, 2015 include the consolidated results of operations of Mercantile Bank Corporation and its consolidated subsidiaries. These subsidiaries include Mercantile Bank of Michigan (“our bank”) and our bank’s two subsidiaries, Mercantile Bank Real Estate Co., LLC (“our real estate company”) and Mercantile Insurance Center, Inc. (“our insurance center”). These consolidated financial statements have been prepared in accordance with the instructions for Form 10-Q and Item 303(b) of Regulation S-K and do not include all disclosures required by accounting principles generally accepted in the United States of America for a complete presentation of our financial condition and results of operations. In the opinion of management, the information reflects all adjustments (consisting only of normal recurring adjustments) which are necessary in order to make the financial statements not misleading and for a fair presentation of the results of operations for such periods. The results for the period ended June 30, 2015 should not be considered as indicative of results for a full year. For further information, refer to the consolidated financial statements and footnotes included in our annual report on Form 10-K for the year ended December 31, 2014. We have five separate business trusts that were formed to issue trust preferred securities. Subordinated debentures were issued to the trusts in return for the proceeds raised from the issuance of the trust preferred securities. The trusts are not consolidated, but instead we report the subordinated debentures issued to the trusts as a liability.
Earnings Per Share, Policy [Policy Text Block]	Earnings Per Share: Basic earnings per share is based on the weighted average number of common shares and participating securities outstanding during the period. Diluted earnings per share include the dilutive effect of additional potential common shares issuable under our stock-based compensation plans and are determined using the treasury stock method. Our unvested restricted shares, which contain non-forfeitable rights to dividends whether paid or accrued (i.e., participating securities), are included in the number of shares outstanding for both basic and diluted earnings per share calculations. In the event of a net loss, our unvested restricted shares are excluded from the calculation of both basic and diluted earnings per share. Approximately 100,000 unvested restricted shares were included in determining both basic and diluted earnings per share for the three and six months ended June 30, 2015. In addition, stock options for approximately 108,000 shares of common stock were included in determining diluted earnings per share for the three and six months ended June 30, 2015. Stock options for approximately 91,000 shares of common stock were antidilutive and not included in determining diluted earnings per share for the three and six months ended June 30, 2015. Stock options for approximately 159,000 shares of common stock were included in determining diluted earnings per share for the three and six months ended June 30, 2014. Stock options for approximately 177,000 shares of common stock were antidilutive and not included in determining diluted earnings per share for the three and six months ended June 30, 2014.
Marketable Securities, Policy [Policy Text Block]	Securities: Debt securities classified as held to maturity are carried at amortized cost when management has the positive intent and ability to hold them to maturity. Debt securities are classified as available for sale when they might be sold prior to maturity. Equity securities with readily determinable fair values are classified as available for sale. Securities available for sale are carried at fair value, with unrealized holding gains and losses reported in other comprehensive income, net of tax. Federal Home Loan Bank stock is carried at cost. Interest income includes amortization of purchase premiums and accretion of discounts. Premiums and discounts on securities are amortized or accreted on the level-yield method without anticipating prepayments, except for mortgage-backed securities where prepayments are anticipated. Gains and losses on sales are recorded on the trade date and determined using the specific identification method. Declines in the fair value of debt securities below their amortized cost that are other than temporary (“OTTI”) are reflected in earnings or other comprehensive income, as appropriate. For those debt securities whose fair value is less than their amortized cost, we consider our intent to sell the security, whether it is more likely than not that we will be required to sell the security before recovery and whether we expect to recover the entire amortized cost of the security based on our assessment of the issuer’s financial condition. In analyzing an issuer’s financial condition, we consider whether the securities are issued by the federal government or its agencies, and whether downgrades by bond rating agencies have occurred. If either of the criteria regarding intent or requirement to sell is met, the entire difference between amortized cost and fair value is recognized as impairment through earnings. For debt securities that do not meet the aforementioned criteria, the amount of impairment is split into two components as follows: 1) OTTI related to credit loss, which must be recognized in the income statement, and 2) OTTI related to other factors, such as liquidity conditions in the market or changes in market interest rates, which is recognized in other comprehensive income. The credit loss is defined as the difference between the present value of the cash flows expected to be collected and the amortized cost.
Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]	Loans: Loans that we have the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at the principal balance outstanding, net of deferred loan fees and costs and an allowance for loan losses. Interest income is accrued on the unpaid principal balance. Loan origination fees, net of certain direct origination costs, are deferred and recognized in interest income using the level-yield method without anticipating prepayments. Interest income on commercial loans and mortgage loans is discontinued at the time the loan is 90 days delinquent unless the loan is well-secured and in process of collection. Consumer and credit card loans are typically charged off no later than when they are 120 days past due. Past due status is based on the contractual terms of the loan. In all cases, loans are placed on nonaccrual or charged off at an earlier date if collection of principal and interest is considered doubtful. All interest accrued but not received for loans placed on nonaccrual is reversed against interest income. Interest received on such loans is accounted for on the cash-basis or cost-recovery method, until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured.
Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block]	Loans Held for Sale: Mortgage loans originated and intended for sale in the secondary market are carried at the lower of aggregate cost or market, as determined by outstanding commitments from investors. Net unrealized losses, if any, are recorded as a valuation allowance and charged to earnings. As of June 30, 2015 and December 31, 2014, we determined that the fair value of our mortgage loans held for sale approximated the recorded cost of $2.4 million and $1.6 million, respectively. Loans held for sale are reported as part of our total loans on the balance sheet. Mortgage loans held for sale are generally sold with servicing rights retained. Gains and losses on sales of mortgage loans are based on the difference between the selling price and the carrying value of the related loan sold, which is reduced by the cost allocated to the servicing right. We generally lock in the sale price to the purchaser of the loan at the same time we make a rate commitment to the borrower. These mortgage banking activities are not designated as hedges and are carried at fair value. The net gain or loss on mortgage banking derivatives is included in the gain on sale of loans. Mortgage loans serviced for others totaled approximately $594 million as of June 30, 2015.
Loans and Leases Receivable, Mortgage Banking Activities, Policy [Policy Text Block]	Mortgage Banking Activities: Mortgage loan servicing rights are recognized as assets based on the allocated value of retained servicing rights on mortgage loans sold. Mortgage loan servicing rights are carried at the lower of amortized cost or fair value and are expensed in proportion to, and over the period of, estimated net servicing revenues. Impairment is evaluated based on the fair value of the rights using groupings of the underlying mortgage loans as to interest rates. Any impairment of a grouping is reported as a valuation allowance. Servicing fee income is recorded for fees earned for serving mortgage loans. The fees are based on a contractual percentage of the outstanding principal or a fixed amount per loan and are recorded as income when earned. Amortization of mortgage loan servicing rights is netted against mortgage loan servicing income and recorded in mortgage banking activities in the income statement.
Loans and Leases Receivable, Troubled Debt Restructuring Policy [Policy Text Block]	Troubled Debt Restructurings: A loan is accounted for as a troubled debt restructuring if we, for economic or legal reasons, grant a concession to a borrower considered to be experiencing financial difficulties that we would not otherwise consider. A troubled debt restructuring may involve the receipt of assets from the debtor in partial or full satisfaction of the loan, or a modification of terms such as a reduction of the stated interest rate or balance of the loan, a reduction of accrued interest, an extension of the maturity date or renewal of the loan at a stated interest rate lower than the current market rate for a new loan with similar risk, or some combination of these concessions. Troubled debt restructurings can be in either accrual or nonaccrual status. Nonaccrual troubled debt restructurings are included in nonperforming loans. Accruing troubled debt restructurings are generally excluded from nonperforming loans as it is considered probable that all contractual principal and interest due under the restructured terms will be collected. In accordance with current accounting guidance, loans modified as troubled debt restructurings are, by definition, considered to be impaired loans. Impairment for these loans is measured on a loan-by-loan basis similar to other impaired loans as described above under “Allowance for Loan Losses.” Certain loans modified as troubled debt restructurings may have been previously measured for impairment under a general allowance methodology (i.e., pooling), thus at the time the loan is modified as a troubled debt restructuring the allowance will be impacted by the difference between the results of these two measurement methodologies. Loans modified as troubled debt restructurings that subsequently default are factored into the determination of the allowance in the same manner as other defaulted loans.
Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block]	Allowance for Loan Losses: The allowance for loan losses (“allowance”) is a valuation allowance for probable incurred credit losses. Loan losses are charged against the allowance when we believe the uncollectability of a loan is confirmed. Subsequent recoveries, if any, are credited to the allowance. We estimate the allowance balance required using past loan loss experience, the nature and volume of the portfolio, information about specific borrower situations and estimated collateral values, economic conditions and other factors. Allocations of the allowance may be made for specific loans, but the entire allowance is available for any loan that, in our judgment, should be charged-off. A loan is considered to be impaired when, based on current information and events, it is probable we will be unable to collect the scheduled payments of principal and interest when due according to the contractual terms of the loan agreement. Factors considered in determining impairment include payment status, collateral value and the probability of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. We determine the significance of payment delays and payment shortfalls on a case-by-case basis, taking into consideration all of the circumstances surrounding the loan and the borrower, including the length of delay, the reasons for delay, the borrower’s prior payment record and the amount of the shortfall in relation to the principal and interest owed. Impairment is measured on a loan-by-loan basis for commercial and construction loans by either the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s obtainable market price or the fair value of collateral if the loan is collateral dependent. Large groups of smaller balance homogeneous loans are collectively evaluated for impairment.
Derivatives, Policy [Policy Text Block]	Derivatives: Derivative financial instruments are recognized as assets or liabilities at fair value. The accounting for changes in the fair value of derivatives depends on the use of the derivatives and whether the derivatives qualify for hedge accounting. Used as part of our asset and liability management to help manage interest rate risk, our derivatives have generally consisted of interest rate swap agreements that qualified for hedge accounting. In February 2012, we entered into an interest rate swap agreement that qualifies for hedge accounting. The current outstanding interest rate swap is discussed in more detail in Note 10. We do not use derivatives for trading purposes. Changes in the fair value of derivatives that are designated, for accounting purposes, as a hedge of the variability of cash flows to be received on various loans and are effective are reported in other comprehensive income. They are later reclassified into earnings in the same periods during which the hedged transaction affects earnings and are included in the line item in which the hedged cash flows are recorded. If hedge accounting does not apply, changes in the fair value of derivatives are recognized immediately in current earnings as interest income or expense. If designated as a hedge, we formally document the relationship between derivatives as hedged items, as well as the risk-management objective and the strategy for undertaking hedge transactions. This documentation includes linking cash flow hedges to specific assets and liabilities on the balance sheet. If designated as a hedge, we also formally assess, both at the hedge’s inception and on an ongoing basis, whether the derivative instruments that are used are highly effective in offsetting changes in cash flows of the hedged items. Ineffective hedge gains and losses are recognized immediately in current earnings as noninterest income or expense. We discontinue hedge accounting when we determine the derivative is no longer effective in offsetting changes in the cash flows of the hedged item, the derivative is settled or terminates, or treatment of the derivative as a hedge is no longer appropriate or intended.
Goodwill and Intangible Assets, Policy [Policy Text Block]	Goodwill and Core Deposit Intangible: Goodwill results from business acquisitions and represents the excess of the purchase price over the fair value of acquired tangible assets and liabilities and identifiable intangible assets. Goodwill is assessed at least annually for impairment and any such impairment is recognized in the period identified. A more frequent assessment is performed if conditions in the market place or changes in the company’s organizational structure occur. We use a discounted income approach and a market valuation model, which compares the inherent value of our company to valuations of recent transactions in the market place to determine if our goodwill has been impaired. The core deposit intangible that arose from the Firstbank Corporation acquisition was initially measured at fair value and is being amortized into noninterest expense over a ten-year period using the sum-of-the-years-digits methodology.
New Accounting Pronouncements, Policy [Policy Text Block]	Adoption of New Accounting Standards: In January of 2014, the FASB issued ASU 2014-04, Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. This ASU clarifies that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. The ASU also requires additional related interim and annual disclosures. The guidance in this ASU is effective for annual and interim periods beginning after December 15, 2014. The adoption of this ASU did not have a material effect on our financial position or results of operations. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. This ASU establishes a comprehensive revenue recognition standard for virtually all industries under U.S. GAAP, including those that previously followed industry-specific guidance such as the real estate, construction and software industries. The revenue standard’s core principle is built on the contract between a vendor and a customer for the provision of goods and services. It attempts to depict the exchange of rights and obligations between the parties in the pattern of revenue recognition based on the consideration to which the vendor is entitled. To accomplish this objective, the standard requires five basic steps: i) identify the contract with the customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. This ASU is effective for annual and interim periods beginning after December 15, 2016 with three transition methods available – full retrospective, retrospective and cumulative effect approach. Adoption of this ASU is not expected to have a material effect on our financial position or results of operations. In June 2014, the FASB issued ASU 2014-11, Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures. This ASU requires two accounting changes. First, repurchase-to-maturity transactions will be accounted for as secured borrowing transactions on the balance sheet, rather than sales. Second, for repurchase financing arrangements, the ASU requires separate accounting for a transfer of a financial asset executed contemporaneously with (or in contemplation of) a repurchase agreement with the same counterparty, which also will generally result in secured borrowing accounting for the repurchase agreement. The ASU also introduces new disclosures to increase transparency about the types of collateral pledged for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions that are accounted for as secured borrowings. The ASU also requires a transferor to disclose information about transactions accounted for as a sale in which the transferor retains substantially all of the exposure to the economic return on the transferred financial assets through an agreement with the transferee. The accounting changes and disclosure for certain transactions accounted for as a sale are effective for the first interim or annual period beginning after December 15, 2014. The disclosure for transactions accounted for as secured borrowings is required for annual periods beginning after December 15, 2014, and for interim periods beginning after March 15, 2015. The required disclosures under the ASU are included in Note 7. Adoption of this ASU did not have a material effect on our financial position or results of operations. In August 2014, the FASB issued ASU 2014-14, Classification of Certain Government-Guaranteed Mortgage Loans Upon Foreclosure. This ASU requires that certain government-guaranteed mortgage loans, including those guaranteed by the Federal Housing Administration, be derecognized and that a separate other receivable be recognized upon foreclosure if certain conditions are met. Upon foreclosure on the loans that meet these criteria, a separate receivable should be recorded based on the amount of the loan balance expected to be recovered from the guarantor. The amendments are effective for annual periods, and interim periods within those years, beginning after December 15, 2014. The adoption of this ASU did not have a material effect on our financial position or results of operations.

Accounting Policies, by Policy (Policies)

6 Months Ended

Jun. 30, 2015

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation: The unaudited financial statements for the six months ended June 30, 2015 include the consolidated results of operations of Mercantile Bank Corporation and its consolidated subsidiaries. These subsidiaries include Mercantile Bank of Michigan (“our bank”) and our bank’s two subsidiaries, Mercantile Bank Real Estate Co., LLC (“our real estate company”) and Mercantile Insurance Center, Inc. (“our insurance center”). These consolidated financial statements have been prepared in accordance with the instructions for Form 10-Q and Item 303(b) of Regulation S-K and do not include all disclosures required by accounting principles generally accepted in the United States of America for a complete presentation of our financial condition and results of operations. In the opinion of management, the information reflects all adjustments (consisting only of normal recurring adjustments) which are necessary in order to make the financial statements not misleading and for a fair presentation of the results of operations for such periods. The results for the period ended June 30, 2015 should not be considered as indicative of results for a full year. For further information, refer to the consolidated financial statements and footnotes included in our annual report on Form 10-K for the year ended December 31, 2014.

We have five separate business trusts that were formed to issue trust preferred securities. Subordinated debentures were issued to the trusts in return for the proceeds raised from the issuance of the trust preferred securities. The trusts are not consolidated, but instead we report the subordinated debentures issued to the trusts as a liability.

Earnings Per Share, Policy [Policy Text Block]

Earnings Per Share: Basic earnings per share is based on the weighted average number of common shares and participating securities outstanding during the period. Diluted earnings per share include the dilutive effect of additional potential common shares issuable under our stock-based compensation plans and are determined using the treasury stock method. Our unvested restricted shares, which contain non-forfeitable rights to dividends whether paid or accrued (i.e., participating securities), are included in the number of shares outstanding for both basic and diluted earnings per share calculations. In the event of a net loss, our unvested restricted shares are excluded from the calculation of both basic and diluted earnings per share.

Approximately 100,000 unvested restricted shares were included in determining both basic and diluted earnings per share for the three and six months ended June 30, 2015. In addition, stock options for approximately 108,000 shares of common stock were included in determining diluted earnings per share for the three and six months ended June 30, 2015. Stock options for approximately 91,000 shares of common stock were antidilutive and not included in determining diluted earnings per share for the three and six months ended June 30, 2015.

Stock options for approximately 159,000 shares of common stock were included in determining diluted earnings per share for the three and six months ended June 30, 2014. Stock options for approximately 177,000 shares of common stock were antidilutive and not included in determining diluted earnings per share for the three and six months ended June 30, 2014.

Marketable Securities, Policy [Policy Text Block]

Securities: Debt securities classified as held to maturity are carried at amortized cost when management has the positive intent and ability to hold them to maturity. Debt securities are classified as available for sale when they might be sold prior to maturity. Equity securities with readily determinable fair values are classified as available for sale. Securities available for sale are carried at fair value, with unrealized holding gains and losses reported in other comprehensive income, net of tax. Federal Home Loan Bank stock is carried at cost.

Interest income includes amortization of purchase premiums and accretion of discounts. Premiums and discounts on securities are amortized or accreted on the level-yield method without anticipating prepayments, except for mortgage-backed securities where prepayments are anticipated. Gains and losses on sales are recorded on the trade date and determined using the specific identification method.

Declines in the fair value of debt securities below their amortized cost that are other than temporary (“OTTI”) are reflected in earnings or other comprehensive income, as appropriate. For those debt securities whose fair value is less than their amortized cost, we consider our intent to sell the security, whether it is more likely than not that we will be required to sell the security before recovery and whether we expect to recover the entire amortized cost of the security based on our assessment of the issuer’s financial condition. In analyzing an issuer’s financial condition, we consider whether the securities are issued by the federal government or its agencies, and whether downgrades by bond rating agencies have occurred. If either of the criteria regarding intent or requirement to sell is met, the entire difference between amortized cost and fair value is recognized as impairment through earnings. For debt securities that do not meet the aforementioned criteria, the amount of impairment is split into two components as follows: 1) OTTI related to credit loss, which must be recognized in the income statement, and 2) OTTI related to other factors, such as liquidity conditions in the market or changes in market interest rates, which is recognized in other comprehensive income. The credit loss is defined as the difference between the present value of the cash flows expected to be collected and the amortized cost.

Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]

Loans: Loans that we have the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at the principal balance outstanding, net of deferred loan fees and costs and an allowance for loan losses. Interest income is accrued on the unpaid principal balance. Loan origination fees, net of certain direct origination costs, are deferred and recognized in interest income using the level-yield method without anticipating prepayments.

Interest income on commercial loans and mortgage loans is discontinued at the time the loan is 90 days delinquent unless the loan is well-secured and in process of collection. Consumer and credit card loans are typically charged off no later than when they are 120 days past due. Past due status is based on the contractual terms of the loan. In all cases, loans are placed on nonaccrual or charged off at an earlier date if collection of principal and interest is considered doubtful.

All interest accrued but not received for loans placed on nonaccrual is reversed against interest income. Interest received on such loans is accounted for on the cash-basis or cost-recovery method, until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured.

Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block]

Loans Held for Sale: Mortgage loans originated and intended for sale in the secondary market are carried at the lower of aggregate cost or market, as determined by outstanding commitments from investors. Net unrealized losses, if any, are recorded as a valuation allowance and charged to earnings. As of June 30, 2015 and December 31, 2014, we determined that the fair value of our mortgage loans held for sale approximated the recorded cost of $2.4 million and $1.6 million, respectively. Loans held for sale are reported as part of our total loans on the balance sheet.

Mortgage loans held for sale are generally sold with servicing rights retained. Gains and losses on sales of mortgage loans are based on the difference between the selling price and the carrying value of the related loan sold, which is reduced by the cost allocated to the servicing right. We generally lock in the sale price to the purchaser of the loan at the same time we make a rate commitment to the borrower. These mortgage banking activities are not designated as hedges and are carried at fair value. The net gain or loss on mortgage banking derivatives is included in the gain on sale of loans. Mortgage loans serviced for others totaled approximately $594 million as of June 30, 2015.

Loans and Leases Receivable, Mortgage Banking Activities, Policy [Policy Text Block]

Mortgage Banking Activities: Mortgage loan servicing rights are recognized as assets based on the allocated value of retained servicing rights on mortgage loans sold. Mortgage loan servicing rights are carried at the lower of amortized cost or fair value and are expensed in proportion to, and over the period of, estimated net servicing revenues. Impairment is evaluated based on the fair value of the rights using groupings of the underlying mortgage loans as to interest rates. Any impairment of a grouping is reported as a valuation allowance.

Servicing fee income is recorded for fees earned for serving mortgage loans. The fees are based on a contractual percentage of the outstanding principal or a fixed amount per loan and are recorded as income when earned. Amortization of mortgage loan servicing rights is netted against mortgage loan servicing income and recorded in mortgage banking activities in the income statement.

Loans and Leases Receivable, Troubled Debt Restructuring Policy [Policy Text Block]

Troubled Debt Restructurings: A loan is accounted for as a troubled debt restructuring if we, for economic or legal reasons, grant a concession to a borrower considered to be experiencing financial difficulties that we would not otherwise consider. A troubled debt restructuring may involve the receipt of assets from the debtor in partial or full satisfaction of the loan, or a modification of terms such as a reduction of the stated interest rate or balance of the loan, a reduction of accrued interest, an extension of the maturity date or renewal of the loan at a stated interest rate lower than the current market rate for a new loan with similar risk, or some combination of these concessions. Troubled debt restructurings can be in either accrual or nonaccrual status. Nonaccrual troubled debt restructurings are included in nonperforming loans. Accruing troubled debt restructurings are generally excluded from nonperforming loans as it is considered probable that all contractual principal and interest due under the restructured terms will be collected.

In accordance with current accounting guidance, loans modified as troubled debt restructurings are, by definition, considered to be impaired loans. Impairment for these loans is measured on a loan-by-loan basis similar to other impaired loans as described above under “Allowance for Loan Losses.” Certain loans modified as troubled debt restructurings may have been previously measured for impairment under a general allowance methodology (i.e., pooling), thus at the time the loan is modified as a troubled debt restructuring the allowance will be impacted by the difference between the results of these two measurement methodologies. Loans modified as troubled debt restructurings that subsequently default are factored into the determination of the allowance in the same manner as other defaulted loans.

Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block]

Allowance for Loan Losses: The allowance for loan losses (“allowance”) is a valuation allowance for probable incurred credit losses. Loan losses are charged against the allowance when we believe the uncollectability of a loan is confirmed. Subsequent recoveries, if any, are credited to the allowance. We estimate the allowance balance required using past loan loss experience, the nature and volume of the portfolio, information about specific borrower situations and estimated collateral values, economic conditions and other factors. Allocations of the allowance may be made for specific loans, but the entire allowance is available for any loan that, in our judgment, should be charged-off.

A loan is considered to be impaired when, based on current information and events, it is probable we will be unable to collect the scheduled payments of principal and interest when due according to the contractual terms of the loan agreement. Factors considered in determining impairment include payment status, collateral value and the probability of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. We determine the significance of payment delays and payment shortfalls on a case-by-case basis, taking into consideration all of the circumstances surrounding the loan and the borrower, including the length of delay, the reasons for delay, the borrower’s prior payment record and the amount of the shortfall in relation to the principal and interest owed. Impairment is measured on a loan-by-loan basis for commercial and construction loans by either the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s obtainable market price or the fair value of collateral if the loan is collateral dependent. Large groups of smaller balance homogeneous loans are collectively evaluated for impairment.

Derivatives, Policy [Policy Text Block]

Derivatives: Derivative financial instruments are recognized as assets or liabilities at fair value. The accounting for changes in the fair value of derivatives depends on the use of the derivatives and whether the derivatives qualify for hedge accounting. Used as part of our asset and liability management to help manage interest rate risk, our derivatives have generally consisted of interest rate swap agreements that qualified for hedge accounting. In February 2012, we entered into an interest rate swap agreement that qualifies for hedge accounting. The current outstanding interest rate swap is discussed in more detail in Note 10. We do not use derivatives for trading purposes.

Changes in the fair value of derivatives that are designated, for accounting purposes, as a hedge of the variability of cash flows to be received on various loans and are effective are reported in other comprehensive income. They are later reclassified into earnings in the same periods during which the hedged transaction affects earnings and are included in the line item in which the hedged cash flows are recorded. If hedge accounting does not apply, changes in the fair value of derivatives are recognized immediately in current earnings as interest income or expense.

If designated as a hedge, we formally document the relationship between derivatives as hedged items, as well as the risk-management objective and the strategy for undertaking hedge transactions. This documentation includes linking cash flow hedges to specific assets and liabilities on the balance sheet. If designated as a hedge, we also formally assess, both at the hedge’s inception and on an ongoing basis, whether the derivative instruments that are used are highly effective in offsetting changes in cash flows of the hedged items. Ineffective hedge gains and losses are recognized immediately in current earnings as noninterest income or expense. We discontinue hedge accounting when we determine the derivative is no longer effective in offsetting changes in the cash flows of the hedged item, the derivative is settled or terminates, or treatment of the derivative as a hedge is no longer appropriate or intended.

Goodwill and Intangible Assets, Policy [Policy Text Block]

Goodwill and Core Deposit Intangible: Goodwill results from business acquisitions and represents the excess of the purchase price over the fair value of acquired tangible assets and liabilities and identifiable intangible assets. Goodwill is assessed at least annually for impairment and any such impairment is recognized in the period identified. A more frequent assessment is performed if conditions in the market place or changes in the company’s organizational structure occur. We use a discounted income approach and a market valuation model, which compares the inherent value of our company to valuations of recent transactions in the market place to determine if our goodwill has been impaired.

The core deposit intangible that arose from the Firstbank Corporation acquisition was initially measured at fair value and is being amortized into noninterest expense over a ten-year period using the sum-of-the-years-digits methodology.

New Accounting Pronouncements, Policy [Policy Text Block]

Adoption of New Accounting Standards: In January of 2014, the FASB issued ASU 2014-04, Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. This ASU clarifies that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. The ASU also requires additional related interim and annual disclosures. The guidance in this ASU is effective for annual and interim periods beginning after December 15, 2014. The adoption of this ASU did not have a material effect on our financial position or results of operations.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. This ASU establishes a comprehensive revenue recognition standard for virtually all industries under U.S. GAAP, including those that previously followed industry-specific guidance such as the real estate, construction and software industries. The revenue standard’s core principle is built on the contract between a vendor and a customer for the provision of goods and services. It attempts to depict the exchange of rights and obligations between the parties in the pattern of revenue recognition based on the consideration to which the vendor is entitled. To accomplish this objective, the standard requires five basic steps: i) identify the contract with the customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. This ASU is effective for annual and interim periods beginning after December 15, 2016 with three transition methods available – full retrospective, retrospective and cumulative effect approach. Adoption of this ASU is not expected to have a material effect on our financial position or results of operations.

In June 2014, the FASB issued ASU 2014-11, Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures. This ASU requires two accounting changes. First, repurchase-to-maturity transactions will be accounted for as secured borrowing transactions on the balance sheet, rather than sales. Second, for repurchase financing arrangements, the ASU requires separate accounting for a transfer of a financial asset executed contemporaneously with (or in contemplation of) a repurchase agreement with the same counterparty, which also will generally result in secured borrowing accounting for the repurchase agreement. The ASU also introduces new disclosures to increase transparency about the types of collateral pledged for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions that are accounted for as secured borrowings. The ASU also requires a transferor to disclose information about transactions accounted for as a sale in which the transferor retains substantially all of the exposure to the economic return on the transferred financial assets through an agreement with the transferee. The accounting changes and disclosure for certain transactions accounted for as a sale are effective for the first interim or annual period beginning after December 15, 2014. The disclosure for transactions accounted for as secured borrowings is required for annual periods beginning after December 15, 2014, and for interim periods beginning after March 15, 2015. The required disclosures under the ASU are included in Note 7. Adoption of this ASU did not have a material effect on our financial position or results of operations.

In August 2014, the FASB issued ASU 2014-14, Classification of Certain Government-Guaranteed Mortgage Loans Upon Foreclosure. This ASU requires that certain government-guaranteed mortgage loans, including those guaranteed by the Federal Housing Administration, be derecognized and that a separate other receivable be recognized upon foreclosure if certain conditions are met. Upon foreclosure on the loans that meet these criteria, a separate receivable should be recorded based on the amount of the loan balance expected to be recovered from the guarantor. The amendments are effective for annual periods, and interim periods within those years, beginning after December 15, 2014. The adoption of this ASU did not have a material effect on our financial position or results of operations.