Document And Entity Information
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Note To Financial Statement Details Textual
Financing Receivables, 60 to 89 Days Past Due [Member]
statementnote3securitiesavailableforsaletables
Proceeds from sales of real estate owned and other repossessed collateral
statementnote4loansallowanceforloanlossesandcreditqualitytables
statementnote6earningspershareepstables
Interest expense:
Financing Receivables, Period Past Due [Domain]
statementnote7derivativesandhedgingactivitiestables
us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax
Total derivatives and hedging activities, tax expense (benefit)
Financing Receivables, Period Past Due [Axis]
statementnote8othercomprehensiveincometables
Financing Receivables, 30 to 59 Days Past Due [Member]
statementnote9commitmentsandcontingenciestables
Financing Receivables [Text Block]
statementnote10stockbasedcompensationtables
statementnote11fairvaluemeasurementstables
us-gaap_AvailableForSaleSecuritiesDebtSecurities
Total, fair value
us-gaap_PaymentsToAcquireLoansHeldForInvestment
Loan purchases
statementnote3securitiesavailableforsalesecuritiesavailableforsaledetails
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax
Reclassification adjustment for net gains included in net income, tax expense (benefit)
Past Due Financing Receivables [Table Text Block]
statementnote3securitiesavailableforsalesecuritiesinacontinuousunrealizedlosspositiondetails
Change in accumulated gain (loss) on effective cash flow hedges, tax expense (benefit)
statementnote3securitiesavailableforsalesecuritiesbycontractualmaturitydetails
us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Available-for-sale Securities Pledged as Collateral
statementnote4loansallowanceforloanlossesandcreditqualityloanportfoliodetails
Proceeds from sale of other loans
statementnote4loansallowanceforloanlossesandcreditqualitysummaryofpastdueandnonaccrualloansdetails
us-gaap_InterestAndDividendIncomeOperating
Total interest and dividend income
statementnote4loansallowanceforloanlossesandcreditqualityallowanceforloanlossesbyportfoliosegmentdetails
us-gaap_ProceedsFromSaleOfLoansHeldForInvestment
Proceeds from Sale of Loans Held-for-investment
statementnote4loansallowanceforloanlossesandcreditqualityallowanceforloanlossesbyportfoliosegmentandimpairmentmethodologydetails
statementnote4loansallowanceforloanlossesandcreditqualityimpairedloansdetails
Other interest and dividend income
statementnote4loansallowanceforloanlossesandcreditqualityloansbyriskratingdetails
Available-for-sale securities, at fair value
Fair Value
statementnote4loansallowanceforloanlossesandcreditqualitytdrsbytypeofmodificationdetails
statementnote4loansallowanceforloanlossesandcreditqualitytdrspreandpostmodificationdetails
statementnote4loansallowanceforloanlossesandcreditqualityloansacquiredaccountedforunderasc31030details
statementnote4loansallowanceforloanlossesandcreditqualityloansacquirednotaccountedforusingtheincomerecognitionmodeldetails
statementnote4loansallowanceforloanlossesandcreditqualityunpaidprincipalbalanceandcarryingamountsofasc31030loansdetails
statementnote6earningspershareepsnumberofsharedoutstandingforbasicanddilutedepsdetails
Change in net unrealized gain or loss on available-for-sale securities, tax expense (benefit)
statementnote6earningspershareepsaverageantidilutiveoptionsandwarrantsdetails
statementnote7derivativesandhedgingactivitiesinterestratecapsandswapagreementsusedtohedgevariableratedebtdetails
statementnote8othercomprehensiveincomecomponentsofothercomprehensiveincomelossdetails
Redemption of Federal Home Loan Bank stock
statementnote8othercomprehensiveincomecomponentsofaccumulatedothercomprehensivelossdetails
statementnote9commitmentsandcontingenciesfinancialinstrumentswithcontractamountsthatrepresentcreditriskdetails
statementnote10stockbasedcompensationsummaryofrestrictedshareactivitydetails
statementnote11fairvaluemeasurementsassetsandliabilitiesmeasuredatfairvalueonarecurringbasisdetails
statementnote11fairvaluemeasurementsassetsmeasuredatfairvalueonanonrecurringbasisdetails
statementnote11fairvaluemeasurementsquantitativeinformationdetails
statementnote11fairvaluemeasurementsestimatedfairvalueofthecompanysfinancialinstrumentsdetails
us-gaap_ProceedsFromSaleOfMortgageServicingRightsMSR
Proceeds from Sale of Mortgage Servicing Rights (MSR)
Notes To Financial Statements
Notes To Financial Statements [Abstract]
Investing activities:
Reported Value Measurement [Member]
us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Other liabilities
Other Investments Measured at Net Asset Value [Member]
Interest on available-for-sale securities
Interest and fees on loans
us-gaap_ComprehensiveIncomeNetOfTax
Comprehensive income
us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures
Cancellation and forfeiture of restricted common stock
Preferred stock, shares outstanding (in shares)
Common stock, shares outstanding (in shares)
us-gaap_SharesOutstanding
Balance (in shares)
Balance (in shares)
Interest and dividend income:
Basis of Accounting [Text Block]
us-gaap_CashAndCashEquivalentsAtCarryingValue
Total cash and cash equivalents
Cash and cash equivalents, beginning of period
Cash and cash equivalents, end of period
Short-term investments
Cash and due from banks
us-gaap_DividendsCommonStock
Dividends on common stock at $0.03 per share
Other tax related APIC adjustment
Stock-based compensation
us-gaap_FairValueInputsDiscountRate
Fair Value Inputs, Discount Rate
us-gaap_FairValueInputsPrepaymentRate
Fair Value Inputs, Prepayment Rate
Valuation Technique [Domain]
Concentration Risk Type [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)
Loans by risk rating
us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Common stock repurchased
Concentration Risk Type [Axis]
us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
Conversions between voting common stock and non-voting common stock, net (in shares)
Conversions between voting common stock and non-voting common stock, net
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.
Fair Value Inputs, Assets, Quantitative Information [Table Text Block]
Loans Held-forsale [Member]
Represents loans which are held for sale.
Loans, individually evaluated
us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited
Cancellation and forfeiture of restricted common stock (in shares)
Loans, collectively evaluated
Bank owned life insurance
Supplemental schedule of noncash investing activities:
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_ServicingAssetAtAmortizedValue
Servicing Asset at Amortized Cost
Loan servicing rights
Allowance for Credit Losses on Financing Receivables [Table Text Block]
Recoveries
Real estate owned and other repossessed collateral, net
us-gaap_LiabilitiesAndStockholdersEquity
Total liabilities and shareholders' equity
Retained earnings
Less: Allowance for loan losses
Allowance for loan losses
Beginning balance
Ending balance
nbn_NumberOfDaysNoticeToRedeemSBASecurities
Number of days’ notice to Redeem SBA Securities
Represents the number of days’ notice required to redeem the SBA securities quarterly.
us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Charge-offs
us-gaap_LoansAndLeasesReceivableNetReportedAmount
Loans, net
Accumulated other comprehensive loss
After- tax amount
Loans
Loans
us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
Other noninterest income
us-gaap_NoninterestIncome
Total noninterest income
Mortgage Loans [Member]
Represents mortgage loans.
Other investments measured at net asset value(1)
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.
us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale
Originations of loans held for sale
Bank-owned life insurance income
Bank-owned life insurance income, net
Noninterest income:
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
Net interest and dividend income after provision for loan losses
Provision for loan losses
Net proceeds from sales of loans held for sale
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]
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Measurements, Recurring [Member]
Fair Value, Measurement Frequency [Domain]
Measurement Frequency [Axis]
Changes in other assets and liabilities:
Amendment Flag
us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure
Federal Home Loan Bank advances
Common Stock
Common stock, shares authorized (in shares)
Subordinated debentures
Common stock, shares issued (in shares)
Common stock, par value (in dollars per share)
us-gaap_ShareBasedCompensation
Stock-based compensation
Current Fiscal Year End Date
Document Fiscal Period Focus
Document Fiscal Year Focus
Document Period End Date
Preferred stock, $1.00 par value, 1,000,000 shares authorized; no shares issued and outstanding at March 31, 2017 and June 30, 2016
us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments
Amortization of available-for-sale securities, net
Preferred stock, shares issued (in shares)
Document Type
Other comprehensive loss, net of tax
Other comprehensive income (loss), net of tax
Income tax expense (benefit) related to other comprehensive income (loss)
Preferred stock, shares authorized (in shares)
Document Information [Line Items]
Document Information [Table]
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]
Entity Filer Category
Entity Current Reporting Status
Entity Voluntary Filers
Entity Well-known Seasoned Issuer
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]
Change in accumulated gain (loss) on effective cash flow hedges
Change in accumulated gain (loss) on effective cash flow hedges, pre tax
Adjustments to reconcile net income to net cash provided by operating activities:
Entity Central Index Key
Entity Registrant Name
Assets measured at fair value on a nonrecurring basis
Entity [Domain]
Legal Entity [Axis]
Change in net unrealized gain (loss) on available-for-sale securities
Loans held for sale
Entity Common Stock, Shares Outstanding (in shares)
Additional paid-in capital
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
Fees for other services to customers
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Trading Symbol
Comprehensive Income (Loss) Note [Text Block]
Total shareholders' equity
Balance
Balance
Commitments and contingencies
us-gaap_Liabilities
Total liabilities
us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax
Total derivatives and hedging activities, after-tax amount
US Government Agencies Debt Securities [Member]
Other liabilities
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax
Reclassification adjustment for net gains included in net income, after-tax amount
Change in accumulated gain (loss) on effective cash flow hedges, after-tax amount
Gain (loss) 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_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed
FDIC insurance premiums
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Loans, net
us-gaap_NoninterestExpense
Total noninterest expense
Federal Home Loan Bank stock
Other noninterest expense
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]
Assets
Noninterest expense:
Other comprehensive income, before tax:
Interest Rate Swap [Member]
us-gaap_OtherComprehensiveIncomeLossTax
Total other comprehensive gain (loss), tax expense (benefit)
us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect
Net (decrease) increase in cash and cash equivalents
us-gaap_OtherComprehensiveIncomeLossBeforeTax
Total other comprehensive gain (loss), pre tax
us-gaap_OtherComprehensiveIncomeLossNetOfTax
Total other comprehensive gain (loss), after-tax amount
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Income before income tax expense
us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations
Net cash provided by financing activities
Interest Rate Cap [Member]
us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations
Net cash used in investing activities
Receive Rate
Unrealized (loss) gain on available-for-sale securities
Net cash provided by operating activities
Pay Rate
Strike Rate
us-gaap_DerivativeCollateralRightToReclaimCash
Derivative, Collateral, Right to Reclaim Cash
nbn_GainLossOnSaleOfSBALoansHeldForSale
Gain on sales of SBA and other loans held for sale
The net gain (loss) resulting from the sale of SBA loans held-for-sale.
Capital lease obligation
Financial Instruments [Domain]
us-gaap_FederalHomeLoanBankAdvancesLongTerm
Federal Home Loan Bank advances
us-gaap_PaymentsOfDividendsCommonStock
Dividends paid on common stock
Financial Instrument [Axis]
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.
us-gaap_PaymentsForRepurchaseOfCommonStock
Repurchase of common stock
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]
Cash dividends declared per common share (in dollars per share)
Fair Value, Hierarchy [Axis]
Subordinated debt
Equity Component [Domain]
Preferred Stock [Member]
Common Stock [Member]
Related allowance
Interest income recognized
Interest income recognized, with related allowance
Equity Components [Axis]
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
Other Assets [Member]
Unpaid principal balance, with related allowance
Other Liabilities [Member]
Average recorded investment, with no related allowance
Unpaid principal balance, with no related allowance
us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Total, amortized cost
Asset Class [Axis]
Asset Class [Domain]
Diluted (in shares)
Weighted average shares used in calculation of diluted EPS (in shares)
us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Stock options (in shares)
Incremental shares from assumed exercise of dilutive securities (in shares)
us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Gross Unrealized Losses
Gross Unrealized Gains
Weighted-average shares outstanding:
Amortized Cost
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]
us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings
Repayment of Federal Home Loan Bank advances
Residential Portfolio Segment [Member]
Commercial Portfolio Segment [Member]
Weighted average shares used in calculation of basic EPS (in shares)
Basic (in shares)
us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Unrealized losses, More than 12 months
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 (in dollars per share)
Balance Sheet Location [Domain]
Balance Sheet Location [Axis]
Contractual Interest Rate Reduction [Member]
Scenario, Unspecified [Domain]
Index
us-gaap_ContractuallySpecifiedServicingFeesAmount
Contractually Specified Servicing Fees, Amount
Performance-Based Vesting Over Three Years [Member]
Refers to the performance-based vesting to occur over three years time.
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]
Gain on sale of other loans
The net gain (loss) resulting from sales of other loans during the period.
Minimum [Member]
Range [Axis]
Accounting Policies [Abstract]
Statement of Financial Position [Abstract]
Net increase in short-term borrowings
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
Statement of Cash Flows [Abstract]
Statement of Stockholders' Equity [Abstract]
us-gaap_Deposits
Total deposits
Due after ten years, amortized cost
Due after five years through ten years, amortized cost
Receivable [Domain]
Due after one year through five years, amortized cost
Receivable Type [Axis]
Due within one year, amortized cost
Savings and interest checking
Investments Classified by Contractual Maturity Date [Table Text Block]
Money market
Time
Schedule of Unrealized Loss on Investments [Table Text Block]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
Demand
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
Notional Amount
Repayment of 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.
Income tax expense
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.
us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities
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.
us-gaap_PolicyTextBlockAbstract
Accounting Policies
Net increase in deposits
Major Types of Debt and Equity Securities [Domain]
Statement [Table]
Major Types of Debt and Equity Securities [Axis]
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.
Income Statement [Abstract]
Financing activities:
Class of Stock [Domain]
Class of Stock [Axis]
Award Type [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.
Equity Award [Domain]
Unrealized Loss
Loans, ASC 310-30
The balance of financing receivables of ASC 310-30 loan for impairment.
Gain on sales of residential loans held for sale
Gain on sales of residential loans held for sale
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]
us-gaap_LossContingencyEstimateOfPossibleLoss
Loss Contingency, Estimate of Possible Loss
Schedule of Unvested Restricted Stock Units Roll Forward [Table Text Block]
Loans Rated 7 [Member]
An entity's internal risk assessment as 7.
Loans Rated 1-6 [Member]
An entity's internal risk assessment as having 1-6 risk.
Loans Rated 9 [Member]
An entity's internal risk assessment as 9.
Loans Rated 8 [Member]
An entity's internal risk assessment as 8.
Loans Rated 10 [Member]
An entity's internal risk assessment as 10.
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.
Salaries and employee benefits
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.
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.
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.
Collateralized Mortgage Backed Securities [Member]
Unfunded Commitments Under Lines of Credit [Member]
Represents unfunded commitments under lines of credit.
Commitments to Grant Loans [Member]
Represents commitments to grant loans.
Derivative Contract [Domain]
Collateralized Debt Obligations [Member]
Derivative Instrument [Axis]
Commercial Loan [Member]
Commitments and Contingencies Disclosure [Text Block]
Forfeited, weighted average grant date fair value (in dollars per share)
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)
Unvested at end of period, shares (in shares)
Unvested at beginning of period, shares (in shares)
Granted, weighted average grant date fair value (in dollars per share)
us-gaap_GainLossOnSaleOfPropertyPlantEquipment
Loss on sale and disposal of premises and equipment, net
us-gaap_GainsLossesOnSalesOfOtherRealEstate
(Gain) loss on sale and impairment of real estate owned and other repossessed collateral, net
Granted, shares (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Schedule of Credit Impaired Loans [Table Text Block]
Tabular disclosure of the unpaid principal balance and carrying amount of purchased credit impaired loans.
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Forfeited, shares (in shares)
Proceeds from maturities and principal payments on available-for-sale securities
us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Proceeds from Sale of Available-for-sale Securities
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Vested, shares (in shares)
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.
us-gaap_MortgageLoansInProcessOfForeclosureAmount
Mortgage Loans in Process of Foreclosure, Amount
Mortgage Servicing Rights [Member]
Portfolio segment of the company's total financing receivables related to Mortgage Servicing Rights MSRs.
nbn_RetirementOfCommonStockTaxesPaid
Taxes paid for retirement of common stock and other tax related APIC adjustment
The amount of taxes paid related to the retirement of common stock.
nbn_DerivativeNumberOfContractsTerminatedPriorToMaturity
Derivative, Number of Contracts Terminated Prior to Maturity
Represents the number of derivative contracts terminated prior to maturity.
us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup
Total loans held for sale
Interest Rate Swaps Terminating in July 2033 [Member]
Interest rate swaps which are terminating in July 2033.
Interest Rate Swaps Terminating in July 2023 [Member]
Interest rate swaps which are terminating in July 2023.
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Table Text Block]
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.
Interest Rate Caps Terminating in September 2019 [Member]
Interest rate caps which are terminating in September 2019.
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]
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield
Beginning balance
Ending balance
Internal Credit Assessment [Axis]
us-gaap_PaymentsToAcquireAvailableForSaleSecurities
Purchases of available-for-sale securities
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans
Disposals and other changes
Reclassifications from non-accretable difference to accretable yield
CRA Qualified Investment [Member]
Represents a CRA qualified investment.
Acquisitions
us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion
Accretion
Intangible asset amortization
Amortization of intangible assets
Carrying amount
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net
Transfers and Servicing of Financial Assets [Text Block]
Standby Letters of Credit Risk [Member]
Credit risk of standby letters of credit.
Professional fees
Marketing expense
Liabilities and Shareholders' Equity
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.
us-gaap_Assets
Total assets
Data processing fees
Loan Servicing Rights [Member]
Represents loan servicing rights.
Real Estate Owned and Other Repossessed Collateral [Member]
Represents real estate owned and other repossessed collateral.
us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Loans and Leases Receivable, Impaired, Commitment to Lend
Occupancy and equipment expense
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
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period
Vesting [Domain]
Net income
Net income
Vesting [Axis]
Other assets
Restricted Stock [Member]
Intangible assets, net
Loan acquisition and collection expense
Antidilutive Securities, Name [Domain]
Employee Stock Option [Member]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]
Antidilutive Securities [Axis]
us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Financing Receivable, Modifications, Subsequent Default, Number of Contracts
Number of Contracts
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]
Recorded Investment
Statement of Comprehensive Income [Abstract]
Recorded Investment Pre-Modification
Principal Forgiveness [Member]
Extended Maturity [Member]
us-gaap_InterestExpense
Total interest expense
Loan Restructuring Modification [Axis]
Loan Restructuring Modification [Domain]
Obligation under capital lease agreements
Amortization of subordinated debt issuance costs
Impaired Financing Receivables [Table Text Block]
Premises and equipment, net
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.
Federal Home Loan Bank advances
us-gaap_InterestExpenseSubordinatedNotesAndDebentures
Subordinated debt
Short-term borrowings
us-gaap_TableTextBlock
Notes Tables
Wholesale repurchase agreements
Financing Receivable Credit Quality Indicators [Table Text Block]
Deposits
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
Interest rate caps
Fair Value
Non- Accrual Loans
Past due
Earnings Per Share [Text Block]
Earnings per common share: