Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation The consolidated financial statements include the accounts of the Company and the Bank. All intercompany accounts and transactions have been eliminated in consolidation. Subsequent Events Events occurring subsequent to December 31, 2018 have been evaluated as to their potential impact on the financial statements. Use of Estimates in Preparation of Financial Statements In preparing the financial statements in accordance with accounting principles generally accepted in the United States of America ("GAAP"), Management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities as of the date of the balance sheet and revenues and expenses for the reporting period. Actual results could differ significantly from those estimates. Material estimates that are particularly susceptible to significant change in the near-term relate to the determination of the allowance for loan losses, goodwill, the valuation of mortgage servicing rights, and other-than-temporary impairment of securities. Investment Securities Investment securities are classified as available for sale or held to maturity when purchased. There are no trading account securities. Securities available for sale consist primarily of debt securities which Management intends to hold for indefinite periods of time. They may be used as part of the Bank's funds management strategy, and may be sold in response to changes in interest rates or prepayment risk, changes in liquidity needs, or for other reasons. They are accounted for at fair value, with unrealized gains or losses adjusted through shareholders' equity, net of related income taxes. The cost basis is adjusted for the amortization of premiums and accretion of discounts, computed using the effective interest method over the securities' contractual lives. Securities to be held to maturity consist primarily of debt securities which Management has acquired solely for long-term investment purposes, rather than for purposes of trading or future sale. For securities to be held to maturity, Management has the intent and the Bank has the ability to hold such securities until their respective maturity dates. Such securities are carried at cost adjusted for the amortization of premiums and accretion of discounts, computed using the effective interest method over the securities' contractual lives. Investment securities transactions are accounted for on a settlement date basis; reported amounts would not be materially different from those accounted for on a trade date basis. Gains and losses on the sales of investment securities are determined using the amortized cost of the specifically identified security. For declines in the fair value of individual debt securities available for sale below their cost that are deemed to be other than temporary, where the Bank does not intend to sell the security and it is more likely than not that the Bank will not be required to sell the security before recovery of its amortized cost basis, the other-than-temporary decline in the fair value of the debt security related to 1) credit loss is recognized in earnings and 2) other factors is recognized in other comprehensive income or loss. Credit loss is deemed to exist if the present value of expected future cash flows using the effective rate at acquisition is less than the amortized cost basis of the debt security. For individual debt securities where the Bank intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost, the other-than-temporary impairment is recognized in earnings equal to the entire difference between the security's cost basis and its fair value at the balance sheet date. Derivative Financial Instruments Designated as Hedges The Company recognizes all derivatives in the consolidated balance sheets at fair value. On the date the Bank enters into the derivative contract, the Company designates the derivative as a hedge of either a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (“cash flow hedge”), a hedge of the fair value of a recognized asset or liability or of an unrecognized firm commitment (“fair value hedge”), or a held for trading instrument (“trading instrument”). The Bank formally documents relationships between hedging instruments and hedged items, as well as its risk management objectives and strategy for undertaking various hedge transactions. The Company also assesses, both at the hedge’s inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are effective in offsetting changes in cash flows or fair values of hedged items. Changes in fair value of a derivative that is effective and that qualifies as a cash flow hedge are recorded in other comprehensive income (loss) and are reclassified into earnings when the forecasted transaction or related cash flows affect earnings. Changes in fair value of a derivative that qualifies as a fair value hedge and the change in fair value of the hedged item are both recorded in earnings and offset each other when the transaction is effective. Those derivatives that are classified as trading instruments are recorded at fair value with changes in fair value recorded in earnings. The Company discontinues hedge accounting when it determines that the derivative is no longer effective in offsetting changes in the cash flows of the hedged item, that it is unlikely that the forecasted transaction will occur, or that the designation of the derivative as a hedging instrument is no longer appropriate. Loans Held for Sale Loans held for sale consist of residential real estate mortgage loans and are carried at the lower of aggregate cost or fair value, as determined by current investor yield requirements. Loans Loans are generally reported at their outstanding principal balances, adjusted for chargeoffs, the allowance for loan losses and any deferred fees or costs to originate loans. Loan commitments are recorded when funded. Loan Fees and Costs Loan origination fees and certain direct loan origination costs are deferred and recognized in interest income as an adjustment to the loan yield over the life of the related loans. The unamortized net deferred fees and costs are included on the balance sheets with the related loan balances, and the amortization is included with the related interest income. Allowance for Loan Losses Loans considered to be uncollectible are charged against the allowance for loan losses. The allowance for loan losses is maintained at a level determined by Management to be appropriate to absorb probable losses. This allowance is increased by provisions charged to operating expenses and recoveries on loans previously charged off. Arriving at an appropriate level of allowance for loan losses necessarily involves a high degree of judgment. In determining the appropriate level of allowance for loan losses, Management takes into consideration several factors, including reviews of individual non-performing loans and performing loans listed on the watch report requiring periodic evaluation, loan portfolio size by category, recent loss experience, delinquency trends and current economic conditions. For all loan classes, loans over 30 days past due are considered delinquent. Impaired loans include restructured loans and loans placed on non-accrual status when, based on current information and events, it is probable that the Bank will be unable to collect all amounts due according to the contractual terms of the loan agreement. These loans are measured at the present value of expected future cash flows discounted at the loan's effective interest rate or at the fair value of the collateral if the loan is collateral dependent. Management takes into consideration impaired loans in addition to the above mentioned factors in determining the appropriate level of allowance for loan losses. Troubled Debt Restructured A troubled debt restructured ("TDR") constitutes a restructuring of debt if the Bank, for economic or legal reasons related to the borrower's financial difficulties, grants a concession to the borrower that it would not otherwise consider. To determine whether or not a loan should be classified as a TDR, Management evaluates a loan to first determine if the borrower demonstrates financial difficulty. Common indicators of this include past due status with bank obligations, substandard credit bureau reports, or an inability to refinance with another lender. If the borrower is experiencing financial difficulty and concessions are granted, such as maturity date extension, interest rate adjustments to below market pricing, or a deferral of payments, the loan will generally be classified as a TDR. Accrual of Interest Income and Expense Interest on loans and investment securities is taken into income using methods which relate the income earned to the balances of loans and investment securities outstanding. Interest expense on liabilities is derived by applying applicable interest rates to principal amounts outstanding. For all classes of loans, recording of interest income on problem loans, which includes impaired loans, ceases when collectibility of principal and interest within a reasonable period of time becomes doubtful. Cash payments received on non-accrual loans, which includes impaired loans, are applied to reduce the loan's principal balance until the remaining principal balance is deemed collectible, after which interest is recognized when collected. As a general rule, a loan may be restored to accrual status when payments are current for a substantial period of time, generally six months, and repayment of the remaining contractual amounts is expected or when it otherwise becomes well secured and in the process of collection. Premises and Equipment Premises, furniture and equipment are stated at cost, less accumulated depreciation. Depreciation expense is computed by straight-line methods over the asset's estimated useful life. Other Real Estate Owned ("OREO") Real estate acquired by foreclosure or deed in lieu of foreclosure is transferred to OREO and recorded at fair value, less estimated costs to sell, based on appraised value at the date actually or constructively received. Loan losses arising from the acquisition of such property are charged against the allowance for loan losses. Subsequent provisions to reduce the carrying value of a property are recorded to the allowance for OREO losses and a charge to operations on a property specific basis. Goodwill and Identified Intangible Assets Intangible assets include the excess of the purchase price over the fair value of net assets acquired (goodwill) from the acquisition of FNB Bankshares in 2005 as well as the core deposit intangible related to the same acquisition. The core deposit intangible related to this acquisition was fully amortized in 2015. Intangible assets also include the goodwill and core deposit intangible from the 2012 acquisition of a bank branch in Rockland, Maine and a bank building in Bangor, Maine. The core deposit intangible will be amortized on a straight-line basis over ten years. Annual amortization expense for each of 2018, 2017 and 2016 was $43,000, and the amortization expense for each year until fully amortized (presently expected to be 2022) will be $43,000. The straight-line basis is used because the Company does not expect significant run off in the core deposits acquired. The Company annually evaluates goodwill, and periodically evaluates other intangible assets, for impairment. At December 31, 2018, the Company determined goodwill and other intangible assets were not impaired. Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between financial statement carrying amounts of assets and liabilities and their respective tax bases, and for tax credits that are available to offset future taxable income. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period the change is enacted. On December 22, 2017 the Tax Cuts and Jobs Act of 2017 ("TCJA") was enacted. One facet of TCJA reduced the federal corporate income tax rate from 35% to 21% effective January 1, 2018. As a result of this legislation, the Company evaluated its deferred tax assets and deferred tax liabilities. The effect of the new corporate income tax rate reduced the value of our net tax deferred assets by $134,000, and a charge to earnings was recorded for this amount in the fourth quarter of 2017. Loan Servicing Servicing rights are recognized when they are acquired through sale of loans. Capitalized servicing rights are reported in other assets and are amortized into non-interest income in proportion to, and over the period of, the estimated future net servicing income of the underlying financial assets. Servicing rights are evaluated for impairment based upon the fair value of the rights as compared to amortized cost. Impairment is determined by stratifying rights by predominant characteristics, such as interest rates and terms. Impairment is recognized through a valuation allowance for an individual stratum, to the extent that fair value is less than the capitalized amount for the stratum. Post-Retirement Benefits The cost of providing post-retirement benefits is accrued during the active service period of the employee or director. Earnings Per Share Basic earnings per share data are based on the weighted average number of common shares outstanding during each year. Diluted earnings per share gives effect to restricted stock granted and stock options and warrants outstanding, determined by the treasury stock method. Comprehensive Income (Loss) Comprehensive income (loss) includes net income and other comprehensive income (loss), which is comprised of the change in unrealized gains and losses on securities available for sale, net of tax, change in unrealized losses on securities transferred from available for sale to held to maturity, net of amortization, change in unrealized gain on cash flow hedging derivative instruments, net of tax, and unrecognized gains and losses related to post-retirement benefit costs, net of tax. Segments The First Bancorp, Inc., through the branches of its subsidiary, First National Bank, provides a broad range of financial services to individuals and companies in coastal Maine. These services include demand, time, and savings deposits; lending; ATM processing; and investment management and trust services. Operations are managed and financial performance is evaluated on a corporate-wide basis. Accordingly, all of the Company's banking operations are considered by Management to be aggregated in one reportable operating segment.