Document And Entity Information
Note To Financial Statement Details Textual
statementsignificantaccountingpoliciespolicies
statementnote2securitiesavailableforsaletables
statementnote3loansallowanceforloanlossesandcreditqualitytables
Interest expense:
statementnote4transfersandservicingoffinancialassetstables
statementnote5premisesandequipmenttables
statementnote6intangibleassetstables
statementnote7depositstables
statementnote8borrowingstables
us-gaap_AvailableForSaleSecuritiesDebtSecurities
Total, fair value
statementnote9subordinateddebttables
Weighted Average Interest Rate, 2018
statementnote10capitalandregulatorymatterstables
Weighted Average Interest Rate, 2017
statementnote11earningspercommonshareepstables
us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Available-for-sale Securities Pledged as Collateral
statementnote12incometaxestables
statementnote14stockbasedcompensationtables
statementnote15commitmentscontingentliabilitiesandotheroffbalancesheetriskstables
Interest and dividend income
us-gaap_InterestAndDividendIncomeOperating
Total interest and dividend income
statementnote16othercomprehensiveincomelosstables
statementnote17derivativestables
statementnote18fairvaluemeasurementstables
Other income
Other interest and dividend income
statementnote19condensedparentinformationtables
Available-for-sale securities, at fair value
Fair Value
statementnote20quarterlyresultsofoperationsunauditedtables
Carrying Amount, 2018
statementnote2securitiesavailableforsalesecuritiesavailableforsaledetails
statementnote2securitiesavailableforsalesecuritiesinacontinuousunrealizedlosspositiondetails
statementnote2securitiesavailableforsalesecuritiesbycontractualmaturitydetails
statementnote3loansallowanceforloanlossesandcreditqualityloanportfoliodetails
statementnote3loansallowanceforloanlossesandcreditqualitysummaryofpastdueandnonaccrualloansdetails
statementnote3loansallowanceforloanlossesandcreditqualityallowanceforloanlossesbyportfoliosegmentdetails
us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds
Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds
statementnote3loansallowanceforloanlossesandcreditqualityallowanceforloanlossesbyportfoliosegmentandimpairmentmethodologydetails
statementnote3loansallowanceforloanlossesandcreditqualityimpairedloansdetails
statementnote3loansallowanceforloanlossesandcreditqualityloansbyriskratingdetails
statementnote3loansallowanceforloanlossesandcreditqualitytdrsbytypeofmodificationdetails
us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged
statementnote3loansallowanceforloanlossesandcreditqualitytdrspreandpostmodificationdetails
statementnote3loansallowanceforloanlossesandcreditqualityloansacquiredaccountedforunderasc31030details
statementnote3loansallowanceforloanlossesandcreditqualityloansacquirednotaccountedforusingtheincomerecognitionmodeldetails
Weighted Average Interest Rate
statementnote3loansallowanceforloanlossesandcreditqualityunpaidprincipalbalanceandcarryingamountsofasc31030loansdetails
statementnote4transfersandservicingoffinancialassetsmortgageservicingactivitiesdetails
statementnote4transfersandservicingoffinancialassetssbaservicingrightsactivitiesdetails
statementnote5premisesandequipmentpremisesandequipmentdetails
statementnote6intangibleassetschangesinthecarryingamountofthecoredepositintangibledetails
statementnote6intangibleassetscomponentsofcoredepositdetails
statementnote6intangibleassetsannualamortizationexpenseassociatedwiththecoredepositintangibledetails
statementnote7depositscompositionofdepositsdetails
statementnote7depositsscheduledmaturitiesoftimecertificatesbyfiscalyeardetails
statementnote8borrowingsadvancesfromfhlbbdetails
statementnote8borrowingsoutstandingcapitalleaseobligationsdetails
statementnote9subordinateddebtjuniorsubordinateddebenturesdetails
statementnote10capitalandregulatorymattersregulatorycapitalratiosdetails
statementnote11earningspercommonshareepsnumberofsharedoutstandingforbasicanddilutedepsdetails
statementnote11earningspercommonshareepsaverageantidilutiveoptionsandwarrantsdetails
Interest on available-for-sale securities
statementnote12incometaxescurrentanddeferredcomponentsofincometaxexpensedetails
statementnote12incometaxesreconciliationbetweenthestatutoryfederalincometaxrateandtheeffectiveincometaxratedetails
us-gaap_InvestmentsInAndAdvancesToAffiliatesAmountOfEquity
Investments in and Advances to Affiliates, Amount of Equity
statementnote12incometaxesdeferredtaxassetsdetails
Interest and fees on loans
statementnote12incometaxesuncertaintaxpositionsdetails
statementnote14stockbasedcompensationstockoptionactivitydetails
statementnote14stockbasedcompensationfairvalueassumptionsdetails
statementnote14stockbasedcompensationstockoptionsoutstandingdetails
statementnote14stockbasedcompensationsummaryofrestrictedstockactivitydetails
Investment in subsidiary
us-gaap_EquityMethodInvestments
statementnote14stockbasedcompensationpretaxstockbasedcompensationexpensedetails
Investment in common securities of affiliated trusts
us-gaap_AdvancesToAffiliate
statementnote15commitmentscontingentliabilitiesandotheroffbalancesheetrisksfinancialinstrumentswithcontractamountsthatrepresentcreditriskdetails
statementnote15commitmentscontingentliabilitiesandotheroffbalancesheetrisksfutureminimumleasepaymentsdetails
Federal Home Loan Bank Branch [Domain]
statementnote16othercomprehensiveincomelosscomponentsofothercomprehensiveincomelossdetails
Federal Home Loan Bank Branch [Axis]
statementnote16othercomprehensiveincomelosscomponentsofaccumulatedothercomprehensivelossdetails
Federal Home Loan Bank of Boston [Member]
statementnote17derivativesandhedgingactivitiesinterestratecapsandswapagreementsusedtohedgevariableratedebtdetails
statementnote17derivativesamountsrecognizedinincomerelatedtobothhedgeineffectivenessandamountsexcludedfromeffectivenesstestingdetails
statementnote18fairvaluemeasurementsassetsandliabilitiesmeasuredatfairvalueonarecurringbasisdetails
statementnote18fairvaluemeasurementsassetsmeasuredatfairvalueonanonrecurringbasisdetails
statementnote18fairvaluemeasurementsquantitativeinformationdetails
Schedule of Federal Home Loan Bank, Advances, by Branch of FHLB Bank [Table Text Block]
statementnote18fairvaluemeasurementsestimatedfairvalueofthecompanysfinancialinstrumentsdetails
statementnote19condensedparentinformationbalancesheetsdetails
statementnote19condensedparentinformationstatementsofincomedetails
statementnote19condensedparentinformationstatementsofcashflowsdetails
statementnote20quarterlyresultsofoperationsunauditedquarterlyfinancialinformationdetails
Use of Estimates, Policy [Policy Text Block]
Notes To Financial Statements
Notes To Financial Statements [Abstract]
New Accounting Pronouncements, Policy [Policy Text Block]
Reclassification, Policy [Policy Text Block]
Interest and dividend income:
Consolidation, Policy [Policy Text Block]
us-gaap_CashAndCashEquivalentsAtCarryingValue
Total cash and cash equivalents
Cash and cash equivalents, beginning of year
Cash and cash equivalents, end of year
Short-term investments
Cash and due from banks
Cash
us-gaap_Cash
Cash, beginning of year
Cash, end of year
Pension and Other Postretirement Benefits Disclosure [Text Block]
Time certificates of greater than or equal to $100 thousand
us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability
Deferred Compensation Arrangement with Individual, Recorded Liability
us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
Deferred Compensation Arrangement with Individual, Compensation Expense
Concentration Risk Type [Domain]
Vests In Three Equal Installments After May 26, 2020 [Member]
Related to the restricted shares that vest in three equal installments after May 26, 2020.
Loans by risk rating
Exercised, weighted average exercise price (in dollars per share)
nbn_SharebasedCompensationArrangementsBySharebasedPaymentAwardOptionsExercisableExercisesInPeriodWeightedAverageExercisePrice
Weighted average price at which option holders acquired shares when converting their exercisable stock options into shares.
Concentration Risk Type [Axis]
Capital contribution
nbn_CapitalContribution
The cash inflow or outflow in related to the capital contribution.
Thereafter
2019
2021
2020
2018
Loans Held-forsale [Member]
Represents loans which are held for sale.
Bank-owned life insurance
Capital to Risk Weighted Assets With Capital Conservation Buffer
Total minimum Capital divided by risk weighted assets with capital conservation buffer as defined in the regulations.
Tier 1 Capital to Risk Weighted Assets With Capital Conservation Buffer
Minimum tier 1 capital divided by risk weighted assets with capital conservation buffer as defined by regulations.
Common Equity Tier 1 Capital to Risk Weighted Assets With Capital Conservation Buffer
Minimum percentage of Common Equity Tier One Risk-based Capital to total risk-weighted assets with capital conservation buffer, as defined by regulatory framework.
Servicing rights, net
Servicing Asset at Amortized Cost
Balance
Balance
Tier 1 Capital to Average Assets With Capital Conservation Buffer
Minimum tier 1 Leverage Capital divided by average assets with capital conservation buffer as defined in the regulations.
Loan servicing rights
us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit
Time Deposits, at or Above FDIC Insurance Limit
Real estate owned and other repossessed collateral, net
Time certificates of less than $100 thousand
Deposit Liabilities Disclosures [Text Block]
Less: valuation allowance
Less: Allowance for loan losses
Allowance for loan losses
Beginning balance
Ending balance
us-gaap_LoansAndLeasesReceivableNetReportedAmount
Loans, net
Loans
Loans
us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums
us-gaap_DeferredTaxAssetsNet
Total deferred tax assets
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
Other noninterest income
us-gaap_DeferredIncomeTaxLiabilities
Total deferred tax liability
us-gaap_DeferredTaxAssetsGross
Gross deferred tax asset
Non-interest income
us-gaap_NoninterestIncome
Total noninterest income
us-gaap_DeferredTaxAssetsLiabilitiesNet
Net deferred tax asset
us-gaap_DeferredTaxAssetsOther
Other
Mortgage Loans [Member]
Represents mortgage loans.
nbn_AccretionExpenseNet
Accretion of fair value adjustments
Net amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values.
Bank-owned life insurance income
Bank-owned life insurance income, net
Noninterest income:
Net interest income after provision for loan losses
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
Net interest and dividend income after provision for loan losses
Unrealized loss on derivatives
Provision for loan losses
Provision for loan losses
Interest income (expense) on hedge ineffectiveness and excluded from effectiveness testing
us-gaap_NumberOfReportableSegments
Number of Reportable Segments
Unrealized loss on available for sale securities
us-gaap_ProvisionForLoanLossesExpensed
Provision for Loan Losses Expensed
Net interest income
us-gaap_InterestIncomeExpenseNet
Net interest and dividend income before provision for loan losses
Federal Home Loan Bank stock, at cost
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Allowance for loan losses
Segment Reporting, Policy [Policy Text Block]
Compensation and benefits
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Business Combinations Policy [Policy Text Block]
Stock-based compensation
us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
Earnings Per Share, Policy [Policy Text Block]
Comprehensive Income, Policy [Policy Text Block]
Income Tax, Policy [Policy Text Block]
us-gaap_UnamortizedDebtIssuanceExpense
Unamortized Debt Issuance Expense
Deferred tax assets
Other
us-gaap_DeferredTaxLiabilitiesOther
Intangible assets
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]
Amendment Flag
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2020
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
2019
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
2018
Current Fiscal Year End Date
Unrealized gain on available for sale securities
us-gaap_DeferredTaxLiabilitiesOtherComprehensiveIncome
Document Fiscal Period Focus
us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1
Finite-Lived Intangible Assets, Remaining Amortization Period
Document Fiscal Year Focus
Document Period End Date
Prepaid expenses
us-gaap_FiniteLivedIntangibleAssetUsefulLife
Finite-Lived Intangible Asset, Useful Life
Premises and equipment
Deferred tax liabilities
Document Type
Document Information [Line Items]
Document Information [Table]
Entity Public Float
Entity Filer Category
Entity Current Reporting Status
Schedule of Finite-Lived Intangible Assets [Table Text Block]
Entity Voluntary Filers
Entity Well-known Seasoned Issuer
us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit
State
State
Entity Central Index Key
Entity Registrant Name
us-gaap_DeferredFederalIncomeTaxExpenseBenefit
Federal
Entity [Domain]
Legal Entity [Axis]
Federal
us-gaap_CurrentIncomeTaxExpenseBenefit
Total current provision
Deferred expense (benefit)
Current provision
Entity Common Stock, Shares Outstanding (in shares)
Fees for other services to customers
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Trading Symbol
Comprehensive Income (Loss) Note [Text Block]
us-gaap_SubordinatedBorrowingInterestRate
Subordinated Borrowing, Interest Rate
Intangible Assets, Finite-Lived, Policy [Policy Text Block]
Schedule of Subordinated Borrowing [Table Text Block]
Subordinated Borrowings Disclosure [Text Block]
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Expenses:
Total expense
us-gaap_CostsAndExpenses
FDIC insurance premiums
Non-interest expense
us-gaap_NoninterestExpense
Total noninterest expense
Other noninterest expense
Property, plant and equipment, useful life (Year)
Condensed Financial Information of Parent Company Only Disclosure [Text Block]
Assets Held under Capital Leases [Member]
Assets
Noninterest expense:
Furniture and Fixtures [Member]
Net cash (used in) provided by financing activities
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net cash used in investing activities
us-gaap_NetCashProvidedByUsedInInvestingActivities
Leaseholds and Leasehold Improvements [Member]
Net cash (used in) provided by operating activities
us-gaap_NetCashProvidedByUsedInOperatingActivities
Building [Member]
Property, Plant and Equipment, Type [Domain]
us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect
Net increase in cash and cash equivalents
Property, Plant and Equipment, Type [Axis]
Land [Member]
us-gaap_CashReserveDepositRequiredAndMade
Cash Reserve Deposit Required and Made
Income before income tax expense
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Income before income tax expense
Property, Plant and Equipment, Policy [Policy Text Block]
us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations
Net cash provided by financing activities
us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations
Net cash used in investing activities
Net cash provided by operating activities
Transfers and Servicing of Financial Assets, Policy [Policy Text Block]
us-gaap_PaymentsOfOrdinaryDividends
Dividends paid to shareholders
nbn_GainLossOnSaleOfSBALoansHeldForSale
Gain on sales of SBA and other loans held for sale, net
The net gain (loss) resulting from the sale of SBA loans held-for-sale.
us-gaap_PaymentsOfDividendsCommonStock
Dividends paid on common stock
nbn_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingThresholdRoePercentageOfTargetedReturns
Share-based Compensation Arrangement by Share-based Payment Award, Vesting Threshold, ROE, Percentage of Targeted Returns
Represents the minimum return on equity ("ROE"), as a percentage of targeted returns, that serves as the threshold to determine the vesting in certain defined increments with regard to a share-based payment award.
Derivatives, Policy [Policy Text Block]
us-gaap_PaymentsForRepurchaseOfCommonStock
Repurchase of common stock
Repurchase of common stock
Cash dividends declared per common share (in dollars per share)
Marketable Securities, Available-for-sale Securities, Policy [Policy Text Block]
Concentration Risk, Credit Risk, Policy [Policy Text Block]
Related allowance
Interest income recognized
Interest income recognized, with related allowance
Collateral dependent impaired loans
Recorded investment
Recorded investment, with related allowance
Interest income recognized, with no related allowance
Average recorded investment
Average recorded investment, with related allowance
Recorded investment, with no related allowance
us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Unpaid principal balance
Unpaid principal balance, with related allowance
Average recorded investment, with no related allowance
Unpaid principal balance, with no related allowance
Asset Class [Axis]
Asset Class [Domain]
Diluted (in shares)
Weighted average shares used in calculation of diluted earnings per share (in shares)
us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Stock options (in shares)
Incremental shares from assumed exercise of dilutive securities (in shares)
Weighted-average shares outstanding:
Diluted earnings per share (in dollars per share)
Diluted (in dollars per share)
Class of Financing Receivable, Type [Domain]
Class of Financing Receivable, Type [Axis]
us-gaap_RepaymentsOfLongTermCapitalLeaseObligations
Repayment of capital lease obligation
Consumer Portfolio Segment [Member]
Commercial Real Estate Portfolio Segment [Member]
Unallocated Financing Receivables [Member]
Financing Receivable Portfolio Segment [Domain]
Financing Receivable Portfolio Segment [Axis]
Residential Portfolio Segment [Member]
Commercial Portfolio Segment [Member]
Basic (in shares)
Vest In Full By August 25, 2019 [Member]
Refers to the vesting period to be completed by August 25, 2019.
Vests In Three Equal Installments After August 25, 2019 [Member]
Refers to the share-based compensation that vests in three equal installments after August 25, 2019.
Basic earnings per share (in dollars per share)
Basic (in dollars per share)
Contractual Interest Rate Reduction [Member]
us-gaap_ContractuallySpecifiedServicingFeesAmount
Contractually Specified Servicing Fees, Amount
Loans and Leases Receivable, Real Estate Acquired Through Foreclosure, Policy [Policy Text Block]
Performance-Based Vesting Over Three Years [Member]
Refers to the performance-based vesting to occur over three years time.
Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block]
Issuance of subordinated debt, net of debt issuance costs
Issuance of subordinated debt, net of debt issuance costs
Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]
Cash and Cash Equivalents, Policy [Policy Text Block]
Gain on sale of other loans
The net gain (loss) resulting from sales of other loans during the period.
Significant Accounting Policies [Text Block]
Accounting Policies [Abstract]
us-gaap_UnrecognizedTaxBenefits
Balance, tax positions
Balance, tax positions
Parent Company [Member]
Statement of Financial Position [Abstract]
Net decrease in short-term borrowings
Consolidated Entities [Domain]
Increase for current year tax position, tax positions
Consolidated Entities [Axis]
us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Reduction of tax positions for prior years, tax positions
Condensed Cash Flow Statement [Table Text Block]
Increase for prior year tax position, tax positions
Statement of Cash Flows [Abstract]
Condensed Income Statement [Table Text Block]
Statement of Stockholders' Equity [Abstract]
Condensed Balance Sheet [Table Text Block]
Receivable [Domain]
Receivable Type [Axis]
Quarterly Financial Information [Table Text Block]
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]
Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Summary of Income Tax Contingencies [Table Text Block]
Investments Classified by Contractual Maturity Date [Table Text Block]
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]
Schedule of Unrealized Loss on Investments [Table Text Block]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
Notional Amount
Derivative, Notional Amount
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
Repayment of FHLBB borrowings and wholesale repurchase agreements
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Voting Common Stock [Member]
Common stock securities that do empower a holder to vote on corporate resolutions or the election of directors.
Fair Value Measurements, Nonrecurring [Table Text Block]
SBA loans held for sale
Amount of residential real estate loans receivables held-for-sale that are not part of a disposal group.
Residential real estate loans held for sale
Amount of residential real estate loans receivables held-for-sale that are not part of a disposal group.
Gain on sales of SBA loans
The amount of gain (loss) resulting from a sale of portfolio loans.
Deposits Location [Member]
Detail of accretion of fair value adjustments on deposits.
Loans Location [Member]
Detail of accretion of fair value adjustments on loans.
Transfers from loans to real estate owned and other repossessed collateral, net
Value transferred from loans to real estate owned and other repossesses collateral.
Borrowing Location [Member]
Detail of accretion of fair value adjustments.
nbn_AvailableforSaleSecuritiesEffectiveDuration
Available-for-sale Securities, Effective Duration
Represents the effective duration of an investment.
Purchased Loans [Member]
Loans classified as purchased.
Originated Loans [Member]
Loans classified as originated.
Home Equity Portfolio Segment [Member]
Portfolio segment of the company's total financing receivables related to home equity receivables.
Net increase in deposits
Nonvoting Common Stock [Member]
Schedule of Allowance for Loan Losses by Portfolio Segment and Impairment Methodology [Table Text Block]
Tabular disclosure of allowance for loan losses by portfolio segment and impairment methodology.
Financing activities:
Class of Stock [Domain]
Class of Stock [Axis]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Comprehensive Income (Loss) [Table Text Block]
Allowance for loan losses, ASC 310-30
Amount of valuation allowance for financing receivables that are related to ASC 310-30.
Loans, ASC 310-30
The balance of financing receivables of ASC 310-30 loan for impairment.
Core Deposits [Member]
Finite-Lived Intangible Assets, Major Class Name [Domain]
Unlikely to be Collected Financing Receivable [Member]
Special Mention [Member]
Finite-Lived Intangible Assets by Major Class [Axis]
Doubtful [Member]
Substandard [Member]
Hedging Relationship [Domain]
Other
us-gaap_IncomeTaxReconciliationOtherReconcilingItems
Hedging Relationship [Axis]
Cash Flow Hedging [Member]
us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
us-gaap_LoansAndLeasesReceivableRelatedParties
Loans and Leases Receivable, Related Parties
us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries
Increase in investment of bank subsidiary
us-gaap_IncomeTaxReconciliationTaxExemptIncome
Tax exempt interest income
Schedule of Unvested Restricted Stock Units Roll Forward [Table Text Block]
Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
us-gaap_ProceedsFromSaleOfLoansReceivable
Proceeds from Sale of Loans Receivable
Share-based Compensation, Stock Options, Activity [Table Text Block]
Contractually required payments receivable
Represents the amount of contractually required payments receivable at the acquisition of acquired loan not accounted for as debt securities with the evidence of deterioration of credit quality.
nbn_CertainLoanAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition
Cash flows expected to be collected
Represents the amount of cash flows expected to be collected at the acquisition of acquired loan not accounted for as debt securities with the evidence of deterioration of credit quality.
nbn_NonaccretableDifference
Nonaccretable difference
The amount of nonaccretable difference.
nbn_AccretableYield
Accretable yield
The amount of accretable yield.
Certain Loans Acquired Icome Recognition Model As Debt Securities Acquired During Period in Transfer Not Accounted for Using [Table Text Block]
Tabular disclosure of the loans acquired in a transfer that were not accounted for using the income recognition model.
nbn_CertainLoanAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue
Fair value of loans acquired
Represents the amount of cash flows expected to be collected at the acquisition of acquired loan not accounted for as debt securities with the evidence of deterioration of credit quality.
Loans at end of period
The recorded value of all loan accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable, for which the income recognition model was not applied.
Loans acquired during the period
The recorded value, at the acquisition date, of loan for which the income recognition model was not applied. This relates to loans accounted for as debt securities acquired during the period, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.
us-gaap_IncomeTaxReconciliationTaxCreditsOther
Low-income housing tax credit, net of adoption of ASU 2014-01
State tax, net of federal tax benefit
Expected income tax expense at federal tax rate
Income Tax Disclosure [Text Block]
Schedule of Credit Impaired Loans [Table Text Block]
Tabular disclosure of the unpaid principal balance and carrying amount of purchased credit impaired loans.
Proceeds from maturities and principal payments on available-for-sale securities
us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Proceeds from Sale of Available-for-sale Securities
nbn_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesUnpaidPrincipal
Unpaid principal balance
The undiscounted amount of principal on loans with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.
SBA [Member]
Portfolio segment of the company's total financing receivables related to the United States Small Business Administration (SBA) loans.
Mortgage Servicing Rights [Member]
Portfolio segment of the company's total financing receivables related to Mortgage Servicing Rights MSRs.
us-gaap_CapitalLeasesFutureMinimumPaymentsDue
Total
2021
us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears
2018
us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent
Taxes paid for retirement of common stock
Taxes paid through cancellation of common stock
The amount of taxes paid related to the retirement of common stock.
2020
us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears
2019
us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears
nbn_DerivativeNumberOfContractsTerminatedPriorToMaturity
Derivative, Number of Contracts Terminated Prior to Maturity
Represents the number of derivative contracts terminated prior to maturity.
Pass [Member]
Interest Rate Swaps Terminating in July 2033 [Member]
Interest rate swaps which are terminating in July 2033.
Long-term Debt, Type [Axis]
Interest Rate Swaps Terminating in July 2023 [Member]
Interest rate swaps which are terminating in July 2023.
Interest Rate Swaps Terminating in July 2028 [Member]
Interest rate swaps which are terminating in July 2028.
Interest Rate Caps Terminating in February 2020 [Member]
Interest rate caps which are terminating in February 2020.
Long-term Debt, Type [Domain]
Interest Rate Caps Terminating in September 2019 [Member]
Interest rate caps which are terminating in September 2019.
us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments
Imputed interest
nbn_AccumulatedOtherComprehensiveIncomeLossTaxes
Unrealized loss on available-for-sale securities, tax effect
The tax effect of the accumulated change in equity from transactions and other events and circumstances from non-owner sources.
Internal Credit Assessment [Domain]
Internal Credit Assessment [Axis]
us-gaap_PaymentsToAcquireAvailableForSaleSecurities
Purchases of available-for-sale securities
CRA Qualified Investment [Member]
Represents a CRA qualified investment.
us-gaap_CashPeriodIncreaseDecreaseExcludingExchangeRateEffect
Net (decrease) increase in cash
Commitments to Originate Loans [Member]
Commitments to originate loans.
Standby Letters of Credit Risk [Member]
Credit risk of standby letters of credit.
Proceeds from sales of premises and equipment
Goodwill and Intangible Assets Disclosure [Text Block]
Collateral Dependent Impaired Loans [Member]
Loans classified as impaired which are collateral dependent.
nbn_FairValueInputsUnderlyingCollateralOnImpairedLoans
Fair Value Inputs, Underlying Collateral On Impaired Loans
The market valuation of underlying collateral on impaired loans.
Loan Servicing Rights [Member]
Represents loan servicing rights.
Real Estate Owned and Other Repossessed Collateral [Member]
Represents real estate owned and other repossessed collateral.
Court Ordered Concession [Member]
Loan modification for a court ordered concession.
Rate and Maturity [Member]
Loan modification for a rate and maturity.
Troubled Debt Restructurings On Financing Receivables Recorded Investment [Table Text Block]
Tabular disclosure of the recorded investment in financing receivables and troubled debt restructurings.
us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Purchases and disposals of premises and equipment, net
Net income
Net income
Net income
us-gaap_DebtInstrumentTerm
Debt Instrument, Term
Stock Appreciation Rights (SARs) [Member]
Restricted Stock [Member]
Antidilutive Securities, Name [Domain]
Employee Stock Option [Member]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]
us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment
Antidilutive Securities [Axis]
us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Financing Receivable, Modifications, Subsequent Default, Number of Contracts
Number of Contracts
Recorded Investment
Recorded Investment Pre-Modification
Principal Forgiveness [Member]
Extended Maturity [Member]
Loan Restructuring Modification [Axis]
Income taxes paid, net
Loan Restructuring Modification [Domain]
Impaired Financing Receivables [Table Text Block]
Troubled Debt Restructurings on Financing Receivables [Table Text Block]
nbn_OffbalanceSheetLiabilityFundsCalled
Off-balance Sheet Liability, Funds Called
The amount of funds called from an off-balance sheet liability held by the company.
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Debt Instrument, Basis Spread on Variable Rate
Financing Receivable Credit Quality Indicators [Table Text Block]
Capital lease obligation
nbn_CapitalLeaseObligationFairValue
The fair value amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.
Current
us-gaap_ThresholdPeriodPastDueForWriteoffOfFinancingReceivable
Threshold Period Past Due for Write-off of Financing Receivable
Non- Accrual Loans
Past due
Earnings Per Share [Text Block]
Earnings per common share:
Carrying Amount
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivables, 60 to 89 Days Past Due [Member]
Proceeds from sales of real estate owned and other repossessed collateral
London Interbank Offered Rate (LIBOR) [Member]
Financing Receivables, Period Past Due [Domain]
us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax
Total derivatives and hedging activities, tax expense (benefit)
Financing Receivables, Period Past Due [Axis]
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivables [Text Block]
Variable Rate [Domain]
Variable Rate [Axis]
us-gaap_PaymentsToAcquireLoansHeldForInvestment
Loan purchases
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax
Reclassification adjustment included in net income, tax expense (benefit)
Past Due Financing Receivables [Table Text Block]
Change in accumulated gain (loss) on effective cash flow hedges, tax expense (benefit)
us-gaap_ProceedsFromSaleOfLoansHeldForInvestment
Proceeds from Sale of Loans Held-for-investment
Change in net unrealized gain or loss on available-for-sale securities, tax expense (benefit)
Redemption of Federal Home Loan Bank stock
us-gaap_ProceedsFromSaleOfMortgageServicingRightsMSR
Proceeds from Sale of Mortgage Servicing Rights (MSR)
Investing activities:
Reported Value Measurement [Member]
us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet
(Decrease) increase in other assets and liabilities
us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Other liabilities
Other Investments Measured at Net Asset Value [Member]
us-gaap_ComprehensiveIncomeNetOfTax
Comprehensive income
Forfeiture of restricted common stock
Quarterly Financial Information [Text Block]
Preferred stock, shares outstanding (in shares)
Common stock, shares outstanding (in shares)
us-gaap_SharesOutstanding
Balance (in shares)
Balance (in shares)
us-gaap_DividendsCommonStock
Dividends on common stock at $0.04 per share
Other
Debt Disclosure [Text Block]
Stock-based compensation
us-gaap_FairValueInputsDiscountRate
Fair Value Inputs, Discount Rate
us-gaap_FairValueInputsPrepaymentRate
Fair Value Inputs, Prepayment Rate
Valuation Technique [Domain]
Valuation Technique [Axis]
us-gaap_IncreaseDecreaseInOtherOperatingAssets
Other assets
Income Approach Valuation Technique [Member]
Market Approach Valuation Technique [Member]
us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Common stock repurchased (in shares)
Common stock repurchased
Common stock repurchased
us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
Conversion of voting common stock to non-voting common stock (in shares)
us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities
Conversion of voting common stock to non-voting common stock
nbn_PaymentsForProceedsFromLoanAndLeaseOriginationsPrincipalCollectionsAndPurchasedLoanPaydownsNet
Loan originations, principal collections, and purchased loan paydowns, net
Cash outflow or inflow related to loan originations, principal collections, and purchased loan paydowns, net.
Subordinated Debt [Member]
us-gaap_AllocatedShareBasedCompensationExpense
Allocated Share-based Compensation Expense
Fair Value Inputs, Assets, Quantitative Information [Table Text Block]
Loans, individually evaluated
us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited
Forfeiture of restricted common stock (in shares)
us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Exercised (in shares)
Stock options exercised, net
Loans, collectively evaluated
Supplemental schedule of cash flow information:
Issuance of restricted common stock
Issuance of restricted common stock (in shares)
Allowance for loan losses, collectively evaluated
Allowance for loan losses, individually evaluated
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
Forfeited (in shares)
Granted (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross
Allowance for Credit Losses on Financing Receivables [Table Text Block]
Recoveries
Stock options exercised, net (in shares)
Total liabilities and shareholders’ equity
us-gaap_LiabilitiesAndStockholdersEquity
Total liabilities and shareholders' equity
Retained earnings
us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Charge-offs
Accumulated other comprehensive loss
Net-of-tax amount
Other investments measured at net asset value(1)
us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale
Originations of loans held for sale
Net proceeds from sales of loans held for sale
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Measurements, Recurring [Member]
Fair Value, Measurement Frequency [Domain]
Measurement Frequency [Axis]
Changes in other assets and liabilities:
Property, Plant and Equipment [Table Text Block]
Property, Plant and Equipment Disclosure [Text Block]
Deferred income tax (benefit) expense
Total deferred (benefit) expense
us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure
Federal Home Loan Bank advances
Common Stock
Common stock, shares authorized (in shares)
us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations
Subordinated debt
Common stock, shares issued (in shares)
Common stock, par value (in dollars per share)
Stock-based compensation
us-gaap_ShareBasedCompensation
Stock-based compensation
Amortization of fair value adjustment for borrowings
us-gaap_AmortizationOfDebtDiscountPremium
Preferred stock, $1.00 par value, 1,000,000 shares authorized; no shares issued and outstanding at June 30, 2017 and June 30, 2016
us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments
Amortization of available-for-sale securities, net
Preferred stock, shares issued (in shares)
Other comprehensive loss, net of tax
Other comprehensive income (loss), net of tax
us-gaap_DepreciationDepletionAndAmortization
Depreciation, Depletion and Amortization
Income tax expense (benefit) related to other comprehensive income (loss)
Preferred stock, shares authorized (in shares)
Preferred stock, par value (in dollars per share)
us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent
Total other comprehensive income (loss), before tax
Depreciation of premises and equipment
Estimate of Fair Value Measurement [Member]
Measurement Basis [Axis]
us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesBeforeTax
Total derivatives and hedging activities, pre tax
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax
Reclassification adjustments included in net income
us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesBeforeTaxPortionAttributableToParent
Total derivatives and hedging activities
Portion at Fair Value Measurement [Member]
us-gaap_GainLossOnSaleOfLoansAndLeases
Gain (Loss) on Sale of Loans and Leases
Change in accumulated gain (loss) on effective cash flow hedges
Adjustments to reconcile net income to net cash provided by operating activities:
Assets measured at fair value on a nonrecurring basis
Change in net unrealized (loss) gain on available-for-sale securities
Loans held for sale
Additional paid-in capital
Interest paid
Residential Real Estate, without Home Equity [Member]
Portfolio segment of the company's total financing receivables related to residential financing receivables, not including Home Equity.
Cash and cash equivalents
Shareholders' equity
Shareholders’ equity
Total shareholders' equity
Balance
Balance
Commitments and contingencies (Note 15)
Total liabilities
us-gaap_Liabilities
Total liabilities
us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax
Total derivatives and hedging activities, after-tax amount
US Government Agencies Debt Securities [Member]
Other liabilities
Other liabilities
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax
Reclassification adjustment included in net income, after tax amount
Change in accumulated gain (loss) on effective cash flow hedges, after-tax amount
(Loss) gain recognized on real estate owned and other repossessed collateral, net
The net amount of gain (loss) recognized on real estate owned and other repossessed collateral.
us-gaap_DepositsFairValueDisclosure
Deposits
Operating activities:
Financial instruments which represent credit risks
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability
Statement [Line Items]
Schedule of Fair Value, Off-balance Sheet Risks [Table Text Block]
Financial liabilities:
Interest rate swaps
Fair Value
us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Balance, interest and penalties
Balance, interest and penalties
us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Loans, net
Federal Home Loan Bank stock
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Financial assets:
us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Discount Rate
AOCI Attributable to Parent [Member]
Change in net unrealized gain or loss on available-for-sale securities, after-tax amount
Fair Value, by Balance Sheet Grouping [Table Text Block]
Fair Value Disclosures [Text Block]
Other comprehensive income (loss), before tax:
Interest Rate Swap [Member]
us-gaap_OtherComprehensiveIncomeLossTax
Total other comprehensive income (loss), tax expense (benefit)
us-gaap_OtherComprehensiveIncomeLossBeforeTax
Total other comprehensive income (loss), pre tax
us-gaap_OtherComprehensiveIncomeLossNetOfTax
Total other comprehensive income (loss), after tax amount
Interest Rate Cap [Member]
Receive Rate
us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Total
Unrealized (loss) gain on available-for-sale securities
us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
Equity Method Investment, Other than Temporary Impairment
us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter
Thereafter
us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
2021
Pay Rate
us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
2022
us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears
2019
Strike Rate
Derivative, Cap Interest Rate
us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
2020
us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent
2018
us-gaap_DerivativeCollateralRightToReclaimCash
Derivative, Collateral, Right to Reclaim Cash
Capital lease obligation
Capital lease obligation
Financial Instruments [Domain]
us-gaap_FederalHomeLoanBankAdvancesLongTerm
Federal Home Loan Bank advances
Financial Instrument [Axis]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Inputs, Level 1 [Member]
Retained Earnings [Member]
Fair Value, Inputs, Level 3 [Member]
Additional Paid-in Capital [Member]
Fair Value Hierarchy [Domain]
Fair Value, Hierarchy [Axis]
Subordinated debt
Subordinated debt
Subordinated Debt
Carrying Amount of Junior Subordinated Debentures Issued to Affiliated Trusts
Equity Component [Domain]
us-gaap_DeferredFinanceCostsNet
Debt Issuance Costs, Net
Preferred Stock [Member]
Common Stock [Member]
Equity Components [Axis]
Other Assets [Member]
Other Liabilities [Member]
us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Total, amortized cost
Carrying Amount, 2017
us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Gross Unrealized Losses
Gross Unrealized Gains
Amortized Cost
us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Unrealized losses, More than 12 months
Balance Sheet Location [Domain]
Balance Sheet Location [Axis]
us-gaap_DerivativeRemainingMaturity1
Derivative, Remaining Maturity
Scenario, Unspecified [Domain]
Index
Scenario, Forecast [Member]
us-gaap_DerivativeNumberOfInstrumentsHeld
Derivative, Number of Instruments Held
Scenario [Axis]
Schedule of Derivative Instruments [Table Text Block]
us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year
us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses
Unrealized Losses
us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses
Unrealized losses, less than 12 months
Fair Value, More than 12 months
Fair Value, Less than 12 months
Fair Value
Maximum [Member]
Range [Domain]
Weighted Average [Member]
Minimum [Member]
Range [Axis]
Due after ten years, fair value
Due within one year, fair value
Due after five years through ten years, fair value
Due after one year through five years, fair value
Financial Instruments Subject to Mandatory Redemption, Financial Instrument [Domain]
Schedule of Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Axis]
Total deposits
Total deposits
Due after ten years, amortized cost
Due after five years through ten years, amortized cost
Due after one year through five years, amortized cost
Due within one year, amortized cost
Savings and interest checking
NOW
Money market
nbn_TransferOfAssetsNumberOfAgreementsToRepurchaseBeforeMaturity
Transfer of Assets Number of Agreements to Repurchase Before Maturity
Represents the number of agreements to repurchase before maturity in transfer of financial assets.
Time
Total
Demand
Regular savings
Loss before equity in undistributed net income of subsidiary
us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
Loss before income tax benefit and equity in undistributed net income of subsidiary
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Equity in undistributed net income of subsidiary
us-gaap_IncomeLossFromEquityMethodInvestments
Undistributed earnings of subsidiary
Income tax expense
Income tax expense
Total tax provision
Schedule of Finite-Lived Intangible Assets, Including Goodwill [Table Text Block]
Tabular disclosure of assets, including goodwill, lacking physical substance with a finite life, by either major class or business segment.
us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities
Schedule of Composition of Deposits [Table Text Block]
Tabular disclosure of composition of deposits.
Schedule of Maturities of Time Certificates [Table Text Block]
Tabular disclosure of scheduled maturities of time certificates by fiscal year.
nbn_CapitalLeasesPresentValueOfPaymentsAsPercentageOfFairValueOfProperty
Capital Leases Present Value of Payments as Percentage of Fair Value of Property
Represents the present value of the capital lease payments over a specified period as a percentage of the fair value of the property.
us-gaap_PolicyTextBlockAbstract
Accounting Policies
nbn_FederalHomeLoanBankAdvancesUnpaidPrincipalBalanceSubjectToCallProvisions
Federal Home Loan Bank Advances Unpaid Principal Balance, Subject to Call Provisions
Unpaid principal balance of the Federal Home Loan Bank (FHLB) advances, subject to call provisions.
Unpaid Principal Balance, 2018
Amount of unpaid principal balance advances from Federal Home Loan Bank (FHLBank) maturing in the second fiscal year following the latest fiscal year.
Unpaid Principal Balance, 2017
Amount of unpaid principal balance advances from Federal Home Loan Bank (FHLBank) maturing in the next fiscal year following the latest fiscal year.
Unpaid Principal Balance
Amount of unpaid principal balance borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.
NBN Capital Trust III Debenture maturing March 30, 2034 [Member]
Represents the NBN Capital Trust III debenture, maturing on March 30, 2034.
NBN Capital Trust II Debenture Maturing March 30, 2034 [Member]
Represents the NBN Capital Trust II debenture, maturing on March 30, 2034.
nbn_CommonSecuritiesOfTrust
Common Securities of Trust
Represents the amount of common securities of trust.
NBN Capital Trust IV Debenture maturing February 23, 2035 [Member]
Represents the NBN Capital Trust IV debenture, maturing on February 23, 2035.
NBN Captial Trust III [Member]
Represents the legal entity of NBN Capital Trust III.
Major Types of Debt and Equity Securities [Domain]
Statement [Table]
NBN Capital Trust II [Member]
Represents the legal entity of NBN Capital Trust II.
Major Types of Debt and Equity Securities [Axis]
nbn_TrustPreferredSecuritiesInterestRate
Trust Preferred Securities, Interest Rate
Represents the interest rate of trust preferred securities issued.
NBN Captial Trust IV [Member]
Represents the legal entity of NBN Capital Trust IV.
nbn_DebtInstrumentPercentageIncreaseInVariableRateBasisForRecognitionOfHigherInterestExpense
Debt Instrument, Percentage Increase in Variable Rate Basis for Recognition of Higher Interest Expense
Represents the increase in variable rate basis for recognition of higher interest expense of the debt instrument.
nbn_TrustPreferredSecuritiesLiquidationAmount
Trust Preferred Securities, Liquidation Amount
Represents the per share liquidation amount of the trust preferred securities.
nbn_SubordinatedDebtPercentageOfPurchasePriceToFaceValueOfNotesIssued
Subordinated Debt, Percentage of Purchase Price to Face Value of Notes Issued
Represents the purchase price in comparison to the face value of the notes issued by the company.
NBN Capital Trusts [Member]
Represents NBN Capital Trusts debentures.
Unpaid Principal Balance of Private Trust Securities Issued
Represents the principal balance of trust preferred securities issued.
nbn_SubordinatedDebtPercentageOfRedemptionPriceToOutstandingPrincipal
Subordinated Debt, Percentage of Redemption Price to Outstanding Principal
Represents the redemption price paid to the amount of outstanding principal.
nbn_CommercialRealEstateLoansHeldAsPercentageOfRiskBasedCapital
Commercial Real Estate Loans Held as Percentage of Risk Based Capital
Represents the commercial real estate loans including owner-occupied commercial real estate loans held, expressed as a percentage of total risk-based capital.
Income Statement [Abstract]
nbn_PurchasedLoansAsPercentageOfAggregateLoans
Purchased Loans as Percentage of Aggregate Loans
Represents the purchased loans expressed as a percentage of total loans.
The Bank [Member]
Legal entity for The Bank.
nbn_PercentageOfLoansFundedWithCoreDeposits
Percentage of Loans Funded with Core Deposits
Represents the percentage of loans funded with core deposits which is defined as non-maturity deposits and non-brokered insured time deposits.
Common equity tier 1 capital to risk weighted assets:
Award Type [Axis]
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets
The minimum Tier One Common Equity ratio (Total Tier One Common Equity divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.
nbn_PercentageOfAmountActuallyUsedForPurposesOtherThanToAbsorbLossesSubjectToTaxationInYearInWhichUsed
Percentage of Amount Actually Used for Purposes Other Than to Absorb Losses Subject to Taxation in Year in Which Used
Represents the percentage of amount actually used subject to taxation in the year in which it was used for purposes other than to absorb the losses for which it was established.
Equity Award [Domain]
Common Equity Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets
The Common Equity Tier 1 capital ratio (Common Equity Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.
Unrealized Loss
Unrealized Loss
nbn_IncomeTaxReconciliationNonTaxableBOLIIncome
Non-taxable BOLI income
The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to non-taxable BOLI income under enacted tax laws.
nbn_PercentageOfReserveForLoanLossesRecaptured
Percentage of Reserve for Loan Losses Recaptured
Represents the percentage of reserve for loan losses recaptured.
Time deposit basis differential
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from time deposit basis differential.
Loan basis differential
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from loan basis differential.
Interest on nonperforming loans
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from interest on nonperforming loans.
Capital lease
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from capital leases.
Increase for prior year tax position, interest and penalties
Represents the amount of increase in accrued interest on an underpayment of income taxes and penalties resulting from tax positions taken in prior period tax returns.
Borrowings basis differential
Amount of deferred tax liability attributable to taxable temporary differences from borrowings basis differential.
Increase for current year tax position, interest and penalties
Represents the amount of increase in accrued interest on an underpayment of income taxes and penalties resulting from tax positions in the current period tax returns.
nbn_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccruedDecreasesResultingFromPriorPeriodTaxPositions
Reduction of tax positions for prior years, interest and penalties
Represents the amount of decrease in accrued interest on an underpayment of income taxes and penalties resulting from tax positions taken in prior period tax returns.
Increase for prior year tax position
Represents the amount of increase in unrecognized tax benefits including accrued interest on an underpayment of income taxes and penalties resulting from tax positions taken in prior period tax returns.
nbn_UnrecognizedTaxBenefitsIncludingIncomeTaxPenaltiesAndInterestAccrued
Balance
Balance
Represents the amount of unrecognized tax benefits including accrued interest on an underpayment of income taxes and penalties pertaining to uncertain tax positions taken in tax returns.
Increase for current year tax position
Represents the amount of increase in unrecognized tax benefits including accrued interest on an underpayment of income taxes and penalties resulting from tax positions taken in the current period tax returns.
nbn_UnrecognizedTaxBenefitsIncludingIncomeTaxPenaltiesAndInterestAccruedDecreasesResultingFromPriorPeriodTaxPositions
Reduction of tax positions for prior years
Represents the amount of decrease in unrecognized tax benefits including accrued interest on an underpayment of income taxes and penalties resulting from tax positions taken in prior period tax returns.
nbn_DefinedContributionPlanPeriodOfServiceForParticipantsUnderPlan
Defined Contribution Plan Period of Service for Participants Under Plan
Represents the period of service required for all participants under the defined contribution plan.
nbn_DefinedContributionPlanEligibleAgeForParticipantsUnderPlan
Defined Contribution Plan Eligible Age for Participants Under Plan
Represents the eligible age for all participants under the defined contribution plan.
nbn_DeferredCompensationArrangementWithIndividualNumberOfSeniorOfficers
Deferred Compensation Arrangement with Individual, Number of Senior Officers
Represents the number of senior officers under the deferred compensation arrangement with entity.
nbn_DefinedContributionPlanEmployerMatchEmployeeContribution
Defined Contribution Plan, Employer Match Employee Contribution
Represents the employee contributions (percentage of compensation) which are matched by the employer.
2010 Plan [Member]
Equity based compensation plan of the company.
Restated Plan [Member]
Equity based compensation plan of the company.
Stock Options with Market-based Conditions [Member]
Equity based compensation arrangement of the company.
nbn_SharebasedCompensationArrangementBySharebasedPaymentAwardNumberOfEmployeesToWhomOptionsGranted
Share-based Compensation Arrangement by Share-based Payment Award Number of Employees to Whom Options Granted
Represents the number of employees to whom options were granted under the equity-based compensation plan.
nbn_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsApplicableHurdlePrice
Share-based Compensation Arrangement by Share-based Payment Award, Options Applicable Hurdle Price
Represents the applicable hurdle price of the options, that varies depending on the number of years that have elapsed since the date of grant, immediately before the modification.
Gain on sales of residential loans held for sale
Gain on sales of residential loans held for sale, net
us-gaap_LossContingencyEstimateOfPossibleLoss
Loss Contingency, Estimate of Possible Loss
Number of options exercisable (in shares)
Weighted average remaining life of options outstanding (Year)
Weighted average remaining life of options exercisable (Year)
Weighted average exercise price of options exercisable (in dollars per share)
Forfeited or expired, weighted average exercise price (in dollars per share)
Represents the weighted average grant date fair value of options forfeited or expired as calculated by applying the disclosed option pricing methodology.
nbn_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageGrantDateFairValue
Exercisable, beginning of year, weighted average exercise price (in dollars per share)
Exercisable, end of year, weighted average exercise price (in dollars per share)
Represents the weighted average grant date fair value of options exercisable as calculated by applying the disclosed option pricing methodology.
Weighted average exercise price of options outstanding (in dollars per share)
Number of options outstanding (in shares)
Incremental weighted average fair value per option (in dollars per share)
Represents the incremental weighted average fair value per option under the assumption that is used in valuing an option on its own shares.
Hull-White Option Pricing Model [Member]
The Hull-White fair value valuation method.
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain]
Range Two [Member]
Second range in a sequence of ranges.
Range One [Member]
First range in a sequence of ranges.
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]
Range Four [Member]
Fourth range in a sequence of ranges.
Range Three [Member]
Third range in a sequence of ranges.
Exercise Price Range [Axis]
Range Six [Member]
Sixth range in a sequence of ranges.
Range Five [Member]
Fifth range in a sequence of ranges.
Dividend yield
Salaries and employee benefits
us-gaap_LeaseAndRentalExpense
Operating Leases, Rent Expense
Risk-free interest rate
Accrued interest receivable
Fair value portion as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.
Expected volatility
Project expense, year ended June 30, 2019
Represents the share-based compensation expense projected for the second fiscal year following the reporting date.
Project expense, year ended June 30, 2018
Represents the share-based compensation expense projected for the first fiscal year following the reporting date.
Project expense, year ended June 30, 2021
Represents the share-based compensation expense projected for the fourth fiscal year following the reporting date.
Project expense, year ended June 30, 2020
Represents the share-based compensation expense projected for the third fiscal year following the reporting date.
Project expense, total
This element represents the total projected share-based compensation expense.
Project expense, year ended June 30, 2022
Represents the share-based compensation expense projected for the fifth fiscal year following the reporting date.
Letter of Credit [Member]
Represents a letter of credit.
Collateralized Mortgage Backed Securities [Member]
Expected life (in years) (Year)
Unfunded Commitments Under Lines of Credit [Member]
Represents unfunded commitments under lines of credit.
Derivative Contract [Domain]
Schedule of Fair Value Hedge Ineffectiveness [Table Text Block]
Tabular disclosure of amounts recognized in income related to both hedge ineffectiveness and amounts excluded from effectiveness testing.
Collateralized Debt Obligations [Member]
Derivative Instrument [Axis]
Consumer Loan [Member]
Commercial Loan [Member]
Commitments and Contingencies Disclosure [Text Block]
Forfeited, weighted average grant date fair value (in dollars per share)
us-gaap_ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments
Impairment
Vested, weighted average grant date fair value (in dollars per share)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
Unvested at beginning of period, weighted average grant date fair value (in dollars per share)
Unvested at end of period, weighted average grant date fair value (in dollars per share)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Unvested at beginning of period (in shares)
Unvested at end of period (in shares)
Additions
Granted, weighted average grant date fair value (in dollars per share)
us-gaap_ServicingAssetAtAmortizedValueAmortization1
Amortization
us-gaap_GainsLossesOnSalesOfOtherRealEstate
Loss (gain) recognized on real estate owned, other repossessed collateral and premise and equipment, net
us-gaap_ServicingAssetAtAmortizedValueDisposals
Disposals
Granted (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Servicing Asset at Amortized Cost [Table Text Block]
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Forfeited (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Vested (in shares)
Aggregate intrinsic value of options exercisable
Exercisable, weighted average exercise price (in dollars per share)
Exercisable (in shares)
Exercisable, beginning of year (in shares)
Exercisable, end of year (in shares)
Aggregate intrinsic value of options outstanding
us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup
Total loans held for sale
Vested, weighted average exercise price (in dollars per share)
Bank Owned Life Insurance [Policy Text Block]
Disclosure of accounting policy for bank owned life insurance.
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Table Text Block]
Federal Home Loan Bank Stock [Policy Text Block]
Disclosure of accounting policy of advances made and reported by Federal Home Loan Bank (FHLBank).
Loans Held for Sale and Loan Servicing [Policy Text Block]
Disclosure of accounting policy for loans held for sale and loan servicing.
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Outstanding at beginning of year, weighted average exercise price (in dollars per share)
Outstanding at end of year, weighted average exercise price (in dollars per share)
Vested (in shares)
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield
Beginning balance
Ending balance
Forfeited, weighted average exercise price (in dollars per share)
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans
Disposals and other changes
Reclassifications from non-accretable difference to accretable yield
Granted, weighted average exercise price (in dollars per share)
Acquisitions
Exercised, weighted average exercise price (in dollars per share)
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion
Accretion
Intangible asset amortization
Amortization of intangible assets
Amortization
Carrying amount
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Outstanding at beginning of year (in shares)
Outstanding at end of year (in shares)
Transfers and Servicing of Financial Assets [Text Block]
Forfeited or expired (in shares)
Professional fees
us-gaap_DefinedContributionPlanCostRecognized
Defined Contribution Plan, Cost
Marketing expense
Liabilities and Shareholders' Equity
Total assets
us-gaap_Assets
Total assets
Data processing fees
us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent
us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Loans and Leases Receivable, Impaired, Commitment to Lend
us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Defined Contribution Plan, Employer Matching Contribution, Percent of Match
Occupancy and equipment expense
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized
Share-based Compensation Award, Tranche One [Member]
Tier One Leverage Capital to Average Assets
Vesting [Domain]
Share-based Compensation Award, Tranche Three [Member]
Tier One Leverage Capital Required to be Well Capitalized to Average Assets
Tier One Leverage Capital Required for Capital Adequacy to Average Assets
Tier One Leverage Capital Required for Capital Adequacy to Average Assets
Share-based Compensation Award, Tranche Two [Member]
Plan Name [Axis]
Capital Required to be Well Capitalized to Risk Weighted Assets
Capital Required for Capital Adequacy to Risk Weighted Assets
Capital Required for Capital Adequacy to Risk Weighted Assets
Vesting [Axis]
Common Equity Tier 1 Risk Based Capital to Risk Weighted Assets
Plan Name [Domain]
Other assets
Other assets
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets
Capital to Risk Weighted Assets
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets
Tier One Risk Based Capital to Risk Weighted Assets
Intangible assets, net
Capital
us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense
us-gaap_FiniteLivedIntangibleAssetsNet
Total
Balance
Balance
Total capital to risk weighted assets:
Capital Required to be Well Capitalized
Capital Required for Capital Adequacy
Loan acquisition and collection expense
Tier One Leverage Capital Required to be Well Capitalized
us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Accumulated amortization
Gross carrying amount
Tier 1 capital to average assets:
Common Equity Tier 1 Risk Based Capital Required to be Well Capitalized
Tier One Leverage Capital Required for Capital Adequacy
Tier One Leverage Capital
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy
Statement of Comprehensive Income [Abstract]
Common equity Tier 1 Capital
Tier One Risk Based Capital
Tier 1 capital to risk weighted assets:
Tier One Risk Based Capital Required to be Well Capitalized
Tier One Risk Based Capital Required for Capital Adequacy
Interest expense
us-gaap_InterestExpense
Total interest expense
Obligation under capital lease agreements
Amortization of subordinated debt issuance costs
Amortization of Debt Issuance Costs
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]
Regulatory Capital Requirements under Banking Regulations [Text Block]
Premises and equipment, net
Less accumulated depreciation
Property, plant and equipment, gross
Federal Home Loan Bank advances
Interest expense
us-gaap_InterestExpenseSubordinatedNotesAndDebentures
Subordinated debt
Short-term borrowings
us-gaap_TableTextBlock
Notes Tables
Wholesale repurchase agreements
Deposits
Interest rate caps
Fair Value