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Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies Notes 9 false false R10.htm 000100 - Disclosure - Note 2: Investments in Securities Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecurities Note 2: Investments in Securities Notes 10 false false R11.htm 000110 - Disclosure - Note 3: Loans and Allowance For Loan Losses Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLosses Note 3: Loans and Allowance For Loan Losses Notes 11 false false R12.htm 000120 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssets Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets Notes 12 false false R13.htm 000130 - 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Disclosure - Note 10: Short-term Borrowings Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowings Note 10: Short-term Borrowings Notes 18 false false R19.htm 000190 - Disclosure - Note 11: Federal Reserve Bank Borrowings Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote11FederalReserveBankBorrowings Note 11: Federal Reserve Bank Borrowings Notes 19 false false R20.htm 000200 - Disclosure - Note 12: Subordinated Debentures Issued To Capital Trusts Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote12SubordinatedDebenturesIssuedToCapitalTrusts Note 12: Subordinated Debentures Issued To Capital Trusts Notes 20 false false R21.htm 000210 - Disclosure - Note 13: Subordinated Notes Notes http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote13SubordinatedNotes Note 13: Subordinated Notes Notes 21 false false R22.htm 000220 - Disclosure - Note 14: Income Taxes Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxes Note 14: Income Taxes Notes 22 false false R23.htm 000230 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstruments Note 15: Disclosures About Fair Value of Financial Instruments Notes 23 false false R24.htm 000240 - Disclosure - Note 16: Operating Leases Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote16OperatingLeases Note 16: Operating Leases Notes 24 false false R25.htm 000250 - Disclosure - Note 17: Derivatives and Hedging Activities Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivities Note 17: Derivatives and Hedging Activities Notes 25 false false R26.htm 000260 - Disclosure - Note 18: Commitments and Credit Risk Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRisk Note 18: Commitments and Credit Risk Notes 26 false false R27.htm 000270 - Disclosure - Note 19: Additional Cash Flow Information Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote19AdditionalCashFlowInformation Note 19: Additional Cash Flow Information Notes 27 false false R28.htm 000280 - 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Disclosure - Note 30: Acquisition of Loans, Deposits and Branches Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote30AcquisitionOfLoansDepositsAndBranches Note 30: Acquisition of Loans, Deposits and Branches Notes 38 false false R39.htm 000390 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Nature of Operations and Operating Segments (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesNatureOfOperationsAndOperatingSegmentsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Nature of Operations and Operating Segments (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 39 false false R40.htm 000400 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Use of Estimates (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesUseOfEstimatesPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Use of Estimates (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 40 false false R41.htm 000410 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Principles of Consolidation (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPrinciplesOfConsolidationPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Principles of Consolidation (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 41 false false R42.htm 000420 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Reclassifications (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesReclassificationsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Reclassifications (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 42 false false R43.htm 000430 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Federal Home Loan Bank Stock (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesFederalHomeLoanBankStockPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Federal Home Loan Bank Stock (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 43 false false R44.htm 000440 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Securities (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesSecuritiesPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Securities (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 44 false false R45.htm 000450 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Mortgage Loans Held for Sale (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesMortgageLoansHeldForSalePolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Mortgage Loans Held for Sale (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 45 false false R46.htm 000460 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loans Originated by the Company (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLoansOriginatedByTheCompanyPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loans Originated by the Company (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 46 false false R47.htm 000470 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Allowance For Loan Losses (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesAllowanceForLoanLossesPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Allowance For Loan Losses (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 47 false false R48.htm 000480 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loans Acquired in Business Combinations (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLoansAcquiredInBusinessCombinationsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loans Acquired in Business Combinations (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 48 false false R49.htm 000490 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: FDIC Indemnification Asset (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesFDICIndemnificationAssetPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: FDIC Indemnification Asset (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 49 false false R50.htm 000500 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Other Real Estate Owned and Repossessions (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesOtherRealEstateOwnedAndRepossessionsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Other Real Estate Owned and Repossessions (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 50 false false R51.htm 000510 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Premises and Equipment (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPremisesAndEquipmentPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Premises and Equipment (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 51 false false R52.htm 000520 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Long-lived Asset Impairment (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLongLivedAssetImpairmentPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Long-lived Asset Impairment (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 52 false false R53.htm 000530 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 53 false false R54.htm 000540 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loan Servicing and Origination Fee Income (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLoanServicingAndOriginationFeeIncomePolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Loan Servicing and Origination Fee Income (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 54 false false R55.htm 000550 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stockholders' Equity (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesStockholdersEquityPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stockholders' Equity (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 55 false false R56.htm 000560 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesEarningsPerSharePolicyPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 56 false false R57.htm 000570 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stock Compensation Plans (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesStockCompensationPlansPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stock Compensation Plans (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 57 false false R58.htm 000580 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Cash Equivalents (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesCashEquivalentsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Cash Equivalents (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 58 false false R59.htm 000590 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Income Taxes (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesIncomeTaxesPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Income Taxes (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 59 false false R60.htm 000600 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Derivatives and Hedging Activities (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesDerivativesAndHedgingActivitiesPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Derivatives and Hedging Activities (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 60 false false R61.htm 000610 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Restriction On Cash and Due From Banks (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesRestrictionOnCashAndDueFromBanksPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Restriction On Cash and Due From Banks (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 61 false false R62.htm 000620 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Recent Accounting Pronouncements (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesRecentAccountingPronouncementsPolicies Note 1: Nature of Operations and Summary of Significant Accounting Policies: Recent Accounting Pronouncements (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 62 false false R63.htm 000630 - Disclosure - Note 2: Investments in Securities: Mortgage-backed securities portfolio (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesMortgageBackedSecuritiesPortfolioPolicies Note 2: Investments in Securities: Mortgage-backed securities portfolio (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 63 false false R64.htm 000640 - Disclosure - Note 2: Investments in Securities: Certain investments in debt securities reported at less than historical cost (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesCertainInvestmentsInDebtSecuritiesReportedAtLessThanHistoricalCostPolicies Note 2: Investments in Securities: Certain investments in debt securities reported at less than historical cost (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 64 false false R65.htm 000650 - Disclosure - Note 2: Investments in Securities: Other-than-temporary Impairment (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesOtherThanTemporaryImpairmentPolicies Note 2: Investments in Securities: Other-than-temporary Impairment (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 65 false false R66.htm 000660 - Disclosure - Note 2: Investments in Securities: Credit Losses Recognized On Investments (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesCreditLossesRecognizedOnInvestmentsPolicies Note 2: Investments in Securities: Credit Losses Recognized On Investments (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 66 false false R67.htm 000670 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Loan Portfolio Credit Quality Internal Grading System Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesLoanPortfolioCreditQualityInternalGradingSystemPolicyPolicies Note 3: Loans and Allowance For Loan Losses: Loan Portfolio Credit Quality Internal Grading System Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 67 false false R68.htm 000680 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesRelatedPartyTransactionsDisclosurePolicies Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 68 false false R69.htm 000690 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsBusinessCombinationsPolicyPolicies Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 69 false false R70.htm 000700 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Loss Sharing Agreements (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsLossSharingAgreementsPolicies Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Loss Sharing Agreements (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 70 false false R71.htm 000710 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Acquisition Fair Value and Expected Cash Flows Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsBusinessAcquisitionFairValueAndExpectedCashFlowsPolicyPolicies Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Acquisition Fair Value and Expected Cash Flows Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 71 false false R72.htm 000720 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetPolicyPolicies Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 72 false false R73.htm 000730 - Disclosure - Note 7: Investments in Limited Partnerships: Investments in Affordable Housing Partnerships Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInAffordableHousingPartnershipsPolicyPolicies Note 7: Investments in Limited Partnerships: Investments in Affordable Housing Partnerships Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 73 false false R74.htm 000740 - Disclosure - Note 7: Investments in Limited Partnerships: Investments in Community Development Entities Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInCommunityDevelopmentEntitiesPolicyPolicies Note 7: Investments in Limited Partnerships: Investments in Community Development Entities Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 74 false false R75.htm 000750 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Loans Held for Sale Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueLoansHeldForSalePolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Loans Held for Sale Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 75 false false R76.htm 000760 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Impaired Loans Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueImpairedLoansPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Impaired Loans Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 76 false false R77.htm 000770 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Foreclosed Assets Held for Sale Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueForeclosedAssetsHeldForSalePolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Foreclosed Assets Held for Sale Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 77 false false R78.htm 000780 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value FDIC Indemnification Asset Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueFDICIndemnificationAssetPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value FDIC Indemnification Asset Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 78 false false R79.htm 000790 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value of Financial Instruments Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueOfFinancialInstrumentsPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value of Financial Instruments Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 79 false false R80.htm 000800 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Cash and Cash Equivalents and Federal Home Loan Bank Stock Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueCashAndCashEquivalentsAndFederalHomeLoanBankStockPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Cash and Cash Equivalents and Federal Home Loan Bank Stock Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 80 false false R81.htm 000810 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Loans and Interest Receivable Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueLoansAndInterestReceivablePolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Loans and Interest Receivable Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 81 false false R82.htm 000820 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Deposits and Accrued Interest Payable Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueDepositsAndAccruedInterestPayablePolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Deposits and Accrued Interest Payable Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 82 false false R83.htm 000830 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Federal home Loan Bank Advances Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueFederalHomeLoanBankAdvancesPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Federal home Loan Bank Advances Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 83 false false R84.htm 000840 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Short-Term Borrowings Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueShortTermBorrowingsPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value Short-Term Borrowings Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 84 false false R85.htm 000850 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Subordinated Debentures Issued To Capital Trusts (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsSubordinatedDebenturesIssuedToCapitalTrustsPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Subordinated Debentures Issued To Capital Trusts (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 85 false false R86.htm 000860 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Subordinated Notes (Policies) Notes http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsSubordinatedNotesPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Subordinated Notes (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 86 false false R87.htm 000870 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Commitments and Contingencies, Policy (Policies) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsCommitmentsAndContingenciesPolicyPolicies Note 15: Disclosures About Fair Value of Financial Instruments: Commitments and Contingencies, Policy (Policies) Policies http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPolicies 87 false false R88.htm 000880 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets: Schedule of Intangible Assets and Goodwill (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsAndGoodwillTables Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets: Schedule of Intangible Assets and Goodwill (Tables) Tables 88 false false R89.htm 000890 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Schedule of Earnings Per Share, Basic and Diluted (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesEarningsPerSharePolicyScheduleOfEarningsPerShareBasicAndDilutedTables Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Schedule of Earnings Per Share, Basic and Diluted (Tables) Tables 89 false false R90.htm 000900 - Disclosure - Note 2: Investments in Securities: Schedule of Available-for-sale Securities Reconciliation (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfAvailableForSaleSecuritiesReconciliationTables Note 2: Investments in Securities: Schedule of Available-for-sale Securities Reconciliation (Tables) Tables 90 false false R91.htm 000910 - Disclosure - Note 2: Investments in Securities: Investments Classified by Contractual Maturity Date (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesInvestmentsClassifiedByContractualMaturityDateTables Note 2: Investments in Securities: Investments Classified by Contractual Maturity Date (Tables) Tables 91 false false R92.htm 000920 - Disclosure - Note 2: Investments in Securities: Held to Maturity Securities (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesHeldToMaturitySecuritiesTables Note 2: Investments in Securities: Held to Maturity Securities (Tables) Tables 92 false false R93.htm 000930 - Disclosure - Note 2: Investments in Securities: Contractual Obligation, Fiscal Year Maturity Schedule (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesContractualObligationFiscalYearMaturityScheduleTables Note 2: Investments in Securities: Contractual Obligation, Fiscal Year Maturity Schedule (Tables) Tables 93 false false R94.htm 000940 - Disclosure - Note 2: Investments in Securities: Schedule of Financial Instruments Owned and Pledged as Collateral (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfFinancialInstrumentsOwnedAndPledgedAsCollateralTables Note 2: Investments in Securities: Schedule of Financial Instruments Owned and Pledged as Collateral (Tables) Tables 94 false false R95.htm 000950 - Disclosure - Note 2: Investments in Securities: Unrealized Gain (Loss) on Investments (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesUnrealizedGainLossOnInvestmentsTables Note 2: Investments in Securities: Unrealized Gain (Loss) on Investments (Tables) Tables 95 false false R96.htm 000960 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Loans (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansTables Note 3: Loans and Allowance For Loan Losses: Schedule of Loans (Tables) Tables 96 false false R97.htm 000970 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Classes of Loans by Aging (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesClassesOfLoansByAgingTables Note 3: Loans and Allowance For Loan Losses: Classes of Loans by Aging (Tables) Tables 97 false false R98.htm 000980 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Financing Receivables NonAccrual Status (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfFinancingReceivablesNonAccrualStatusTables Note 3: Loans and Allowance For Loan Losses: Schedule of Financing Receivables NonAccrual Status (Tables) Tables 98 false false R99.htm 000990 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Loans and Leases Receivable Allowance for Loan Losses (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansAndLeasesReceivableAllowanceForLoanLossesTables Note 3: Loans and Allowance For Loan Losses: Schedule of Loans and Leases Receivable Allowance for Loan Losses (Tables) Tables 99 false false R100.htm 001000 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Impaired Financing Receivables (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesImpairedFinancingReceivablesTables Note 3: Loans and Allowance For Loan Losses: Impaired Financing Receivables (Tables) Tables 100 false false R101.htm 001010 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructurings on Financing Receivables (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesTroubledDebtRestructuringsOnFinancingReceivablesTables Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructurings on Financing Receivables (Tables) Tables 101 false false R102.htm 001020 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Financing Receivable Credit Quality Indicators (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesFinancingReceivableCreditQualityIndicatorsTables Note 3: Loans and Allowance For Loan Losses: Financing Receivable Credit Quality Indicators (Tables) Tables 102 false false R103.htm 001030 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure: Schedule of Related Party Transactions (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesRelatedPartyTransactionsDisclosureScheduleOfRelatedPartyTransactionsTables Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure: Schedule of Related Party Transactions (Tables) Tables 103 false false R104.htm 001040 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Business Combination Accretable Yield (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfBusinessCombinationAccretableYieldTables Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Business Combination Accretable Yield (Tables) Tables 104 false false R105.htm 001050 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Impact of Acquired Loans on Financial Results (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfImpactOfAcquiredLoansOnFinancialResultsTables Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Impact of Acquired Loans on Financial Results (Tables) Tables 105 false false R106.htm 001060 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Roll Forward (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetRollForwardTables Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Roll Forward (Tables) Tables 106 false false R107.htm 001070 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy: FDIC Indemnification Asset Roll Forward (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetPolicyFDICIndemnificationAssetRollForwardTables Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy: FDIC Indemnification Asset Roll Forward (Tables) Tables 107 false false R108.htm 001080 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Changes in Accretable Yield for Acquired Loan Pools (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfChangesInAccretableYieldForAcquiredLoanPoolsTables Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Changes in Accretable Yield for Acquired Loan Pools (Tables) Tables 108 false false R109.htm 001090 - Disclosure - Note 5: Other Real Estate Owned: Schedule of major classifications of other real estate owned (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfMajorClassificationsOfOtherRealEstateOwnedTables Note 5: Other Real Estate Owned: Schedule of major classifications of other real estate owned (Tables) Tables 109 false false R110.htm 001100 - Disclosure - Note 5: Other Real Estate Owned: Schedule of expenses applicable to other real estate owned (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfExpensesApplicableToOtherRealEstateOwnedTables Note 5: Other Real Estate Owned: Schedule of expenses applicable to other real estate owned (Tables) Tables 110 false false R111.htm 001110 - Disclosure - Note 6: Premises and Equipment: Property, Plant and Equipment (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote6PremisesAndEquipmentPropertyPlantAndEquipmentTables Note 6: Premises and Equipment: Property, Plant and Equipment (Tables) Tables 111 false false R112.htm 001120 - Disclosure - Note 8: Deposits: Schedule of Deposit Liabilities (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfDepositLiabilitiesTables Note 8: Deposits: Schedule of Deposit Liabilities (Tables) Tables 112 false false R113.htm 001130 - Disclosure - Note 8: Deposits: Maturities of certificates of deposit (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsMaturitiesOfCertificatesOfDepositTables Note 8: Deposits: Maturities of certificates of deposit (Tables) Tables 113 false false R114.htm 001140 - Disclosure - Note 8: Deposits: Schedule of Interest Expense on Deposit Liabilities (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfInterestExpenseOnDepositLiabilitiesTables Note 8: Deposits: Schedule of Interest Expense on Deposit Liabilities (Tables) Tables 114 false false R115.htm 001150 - Disclosure - Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank, Advances (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote9AdvancesFromFederalHomeLoanBankFederalHomeLoanBankAdvancesTables Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank, Advances (Tables) Tables 115 false false R116.htm 001160 - Disclosure - Note 10: Short-term Borrowings: Schedule of Short-term Debt (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfShortTermDebtTables Note 10: Short-term Borrowings: Schedule of Short-term Debt (Tables) Tables 116 false false R117.htm 001170 - Disclosure - Note 10: Short-term Borrowings: Schedule of Repurchase Agreements (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfRepurchaseAgreementsTables Note 10: Short-term Borrowings: Schedule of Repurchase Agreements (Tables) Tables 117 false false R118.htm 001180 - Disclosure - Note 12: Subordinated Debentures Issued To Capital Trusts: Schedule of Subordinated Debentures Issued to Capital Trusts (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote12SubordinatedDebenturesIssuedToCapitalTrustsScheduleOfSubordinatedDebenturesIssuedToCapitalTrustsTables Note 12: Subordinated Debentures Issued To Capital Trusts: Schedule of Subordinated Debentures Issued to Capital Trusts (Tables) Tables 118 false false R119.htm 001190 - Disclosure - Note 13: Subordinated Notes: Schedule of Subordinated Borrowing (Tables) Notes http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote13SubordinatedNotesScheduleOfSubordinatedBorrowingTables Note 13: Subordinated Notes: Schedule of Subordinated Borrowing (Tables) Tables 119 false false R120.htm 001200 - Disclosure - Note 14: Income Taxes: Schedule of Components of Income Tax Expense (Benefit) (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseBenefitTables Note 14: Income Taxes: Schedule of Components of Income Tax Expense (Benefit) (Tables) Tables 120 false false R121.htm 001210 - Disclosure - Note 14: Income Taxes: Schedule of Deferred Tax Assets and Liabilities (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesTables Note 14: Income Taxes: Schedule of Deferred Tax Assets and Liabilities (Tables) Tables 121 false false R122.htm 001220 - Disclosure - Note 14: Income Taxes: Schedule of Effective Income Tax Rate Reconciliation (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationTables Note 14: Income Taxes: Schedule of Effective Income Tax Rate Reconciliation (Tables) Tables 122 false false R123.htm 001230 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets Measured on Recurring Basis (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsMeasuredOnRecurringBasisTables Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets Measured on Recurring Basis (Tables) Tables 123 false false R124.htm 001240 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets and Liabilities Measured on Nonrecurring Basis (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisTables Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets and Liabilities Measured on Nonrecurring Basis (Tables) Tables 124 false false R125.htm 001250 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Schedule Of Financial Instruments Fair Value (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfFinancialInstrumentsFairValueTables Note 15: Disclosures About Fair Value of Financial Instruments: Schedule Of Financial Instruments Fair Value (Tables) Tables 125 false false R126.htm 001260 - Disclosure - Note 16: Operating Leases: Schedule of Future Minimum Rental Payments for Operating Leases (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote16OperatingLeasesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTables Note 16: Operating Leases: Schedule of Future Minimum Rental Payments for Operating Leases (Tables) Tables 126 false false R127.htm 001270 - Disclosure - Note 17: Derivatives and Hedging Activities: Derivative Instruments, Gain (Loss) (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesDerivativeInstrumentsGainLossTables Note 17: Derivatives and Hedging Activities: Derivative Instruments, Gain (Loss) (Tables) Tables 127 false false R128.htm 001280 - Disclosure - Note 17: Derivatives and Hedging Activities: Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTables Note 17: Derivatives and Hedging Activities: Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Tables) Tables 128 false false R129.htm 001290 - Disclosure - Note 19: Additional Cash Flow Information: Schedule of Cash Flow, Supplemental Disclosures (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote19AdditionalCashFlowInformationScheduleOfCashFlowSupplementalDisclosuresTables Note 19: Additional Cash Flow Information: Schedule of Cash Flow, Supplemental Disclosures (Tables) Tables 129 false false R130.htm 001300 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Stock Options, Activity (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationStockOptionsActivityTables Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Stock Options, Activity (Tables) Tables 130 false false R131.htm 001310 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Fair Value Option Pricing Model Assumptions (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfFairValueOptionPricingModelAssumptionsTables Note 21: Stock Compensation Plans: Schedule of Fair Value Option Pricing Model Assumptions (Tables) Tables 131 false false R132.htm 001320 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Activity (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationActivityTables Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Activity (Tables) Tables 132 false false R133.htm 001330 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Nonvested Share Activity (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfNonvestedShareActivityTables Note 21: Stock Compensation Plans: Schedule of Nonvested Share Activity (Tables) Tables 133 false false R134.htm 001340 - Disclosure - Note 21: Stock Compensation Plans: Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableTables Note 21: Stock Compensation Plans: Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable (Tables) Tables 134 false false R135.htm 001350 - Disclosure - Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsInAccumulatedOtherComprehensiveIncomeLossToBeRecognizedOverNextFiscalYearTables Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year (Tables) Tables 135 false false R136.htm 001360 - Disclosure - Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsReclassifiedFromAccumulatedOtherComprehensiveIncomeTables Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Tables) Tables 136 false false R137.htm 001370 - Disclosure - Note 24: Regulatory Matters: Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote24RegulatoryMattersScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTables Note 24: Regulatory Matters: Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Tables) Tables 137 false false R138.htm 001380 - Disclosure - Note 26: Summary of Unaudited Quarterly Operating Results: Schedule of Quarterly Financial Information (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote26SummaryOfUnauditedQuarterlyOperatingResultsScheduleOfQuarterlyFinancialInformationTables Note 26: Summary of Unaudited Quarterly Operating Results: Schedule of Quarterly Financial Information (Tables) Tables 138 false false R139.htm 001390 - Disclosure - Note 27: Condensed Parent Company Statements: Condensed Balance Sheet -- Great Southern Bancorp, Inc. (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote27CondensedParentCompanyStatementsCondensedBalanceSheetGreatSouthernBancorpIncTables Note 27: Condensed Parent Company Statements: Condensed Balance Sheet -- Great Southern Bancorp, Inc. (Tables) Tables 139 false false R140.htm 001400 - Disclosure - Note 27: Condensed Parent Company Statements: Condensed Income Statement -- Great Southern Bancorp, Inc. (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote27CondensedParentCompanyStatementsCondensedIncomeStatementGreatSouthernBancorpIncTables Note 27: Condensed Parent Company Statements: Condensed Income Statement -- Great Southern Bancorp, Inc. (Tables) Tables 140 false false R141.htm 001410 - Disclosure - Note 27: Condensed Parent Company Statements: Condensed Cash Flow Statement -- Great Southern Bancorp, Inc. (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote27CondensedParentCompanyStatementsCondensedCashFlowStatementGreatSouthernBancorpIncTables Note 27: Condensed Parent Company Statements: Condensed Cash Flow Statement -- Great Southern Bancorp, Inc. (Tables) Tables 141 false false R142.htm 001420 - Disclosure - Note 27: Condensed Parent Company Statements: Condensed Statement of Comprehensive Income -- Great Southern Bancorp, Inc. (Tables) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote27CondensedParentCompanyStatementsCondensedStatementOfComprehensiveIncomeGreatSouthernBancorpIncTables Note 27: Condensed Parent Company Statements: Condensed Statement of Comprehensive Income -- Great Southern Bancorp, Inc. 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Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Nature of Operations and Operating Segments (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesNatureOfOperationsAndOperatingSegmentsDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Nature of Operations and Operating Segments (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesNatureOfOperationsAndOperatingSegmentsPolicies 145 false false R146.htm 001460 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Long-lived Asset Impairment (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLongLivedAssetImpairmentDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Long-lived Asset Impairment (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesLongLivedAssetImpairmentPolicies 146 false false R147.htm 001470 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets: Schedule of Intangible Assets and Goodwill (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsAndGoodwillDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Goodwill and Intangible Assets: Schedule of Intangible Assets and Goodwill (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsAndGoodwillTables 147 false false R148.htm 001480 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Schedule of Earnings Per Share, Basic and Diluted (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesEarningsPerSharePolicyScheduleOfEarningsPerShareBasicAndDilutedDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Schedule of Earnings Per Share, Basic and Diluted (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesEarningsPerSharePolicyScheduleOfEarningsPerShareBasicAndDilutedTables 148 false false R149.htm 001490 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Options to Purchase Shares of Common Stock (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesEarningsPerSharePolicyOptionsToPurchaseSharesOfCommonStockDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Earnings Per Share, Policy: Options to Purchase Shares of Common Stock (Details) Details 149 false false R150.htm 001500 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stock Compensation Plans (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesStockCompensationPlansDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Stock Compensation Plans (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesStockholdersEquityPolicies 150 false false R151.htm 001510 - Disclosure - Note 1: Nature of Operations and Summary of Significant Accounting Policies: Restriction On Cash and Due From Banks (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesRestrictionOnCashAndDueFromBanksDetails Note 1: Nature of Operations and Summary of Significant Accounting Policies: Restriction On Cash and Due From Banks (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote1NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesRestrictionOnCashAndDueFromBanksPolicies 151 false false R152.htm 001520 - Disclosure - Note 2: Investments in Securities: Schedule of Available-for-sale Securities Reconciliation (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfAvailableForSaleSecuritiesReconciliationDetails Note 2: Investments in Securities: Schedule of Available-for-sale Securities Reconciliation (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfAvailableForSaleSecuritiesReconciliationTables 152 false false R153.htm 001530 - Disclosure - Note 2: Investments in Securities: Mortgage-backed securities portfolio (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesMortgageBackedSecuritiesPortfolioDetails Note 2: Investments in Securities: Mortgage-backed securities portfolio (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesMortgageBackedSecuritiesPortfolioPolicies 153 false false R154.htm 001540 - Disclosure - Note 2: Investments in Securities: Investments Classified by Contractual Maturity Date (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesInvestmentsClassifiedByContractualMaturityDateDetails Note 2: Investments in Securities: Investments Classified by Contractual Maturity Date (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesInvestmentsClassifiedByContractualMaturityDateTables 154 false false R155.htm 001550 - Disclosure - Note 2: Investments in Securities: Held to Maturity Securities (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesHeldToMaturitySecuritiesDetails Note 2: Investments in Securities: Held to Maturity Securities (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesHeldToMaturitySecuritiesTables 155 false false R156.htm 001560 - Disclosure - Note 2: Investments in Securities: Contractual Obligation, Fiscal Year Maturity Schedule (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesContractualObligationFiscalYearMaturityScheduleDetails Note 2: Investments in Securities: Contractual Obligation, Fiscal Year Maturity Schedule (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesContractualObligationFiscalYearMaturityScheduleTables 156 false false R157.htm 001570 - Disclosure - Note 2: Investments in Securities: Schedule of Financial Instruments Owned and Pledged as Collateral (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfFinancialInstrumentsOwnedAndPledgedAsCollateralDetails Note 2: Investments in Securities: Schedule of Financial Instruments Owned and Pledged as Collateral (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesScheduleOfFinancialInstrumentsOwnedAndPledgedAsCollateralTables 157 false false R158.htm 001580 - Disclosure - Note 2: Investments in Securities: Certain investments in debt securities reported at less than historical cost (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesCertainInvestmentsInDebtSecuritiesReportedAtLessThanHistoricalCostDetails Note 2: Investments in Securities: Certain investments in debt securities reported at less than historical cost (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesCertainInvestmentsInDebtSecuritiesReportedAtLessThanHistoricalCostPolicies 158 false false R159.htm 001590 - Disclosure - Note 2: Investments in Securities: Unrealized Gain (Loss) on Investments (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesUnrealizedGainLossOnInvestmentsDetails Note 2: Investments in Securities: Unrealized Gain (Loss) on Investments (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesUnrealizedGainLossOnInvestmentsTables 159 false false R160.htm 001600 - Disclosure - Note 2: Investments in Securities: Other-than-temporary Impairment: Other than Temporary Impairment of Securities (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesOtherThanTemporaryImpairmentOtherThanTemporaryImpairmentOfSecuritiesDetails Note 2: Investments in Securities: Other-than-temporary Impairment: Other than Temporary Impairment of Securities (Details) Details 160 false false R161.htm 001610 - Disclosure - Note 2: Investments in Securities: Credit Losses Recognized On Investments: Credit Losses Recognized on Investments (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote2InvestmentsInSecuritiesCreditLossesRecognizedOnInvestmentsCreditLossesRecognizedOnInvestmentsDetails Note 2: Investments in Securities: Credit Losses Recognized On Investments: Credit Losses Recognized on Investments (Details) Details 161 false false R162.htm 001620 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Loans (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansDetails Note 3: Loans and Allowance For Loan Losses: Schedule of Loans (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansTables 162 false false R163.htm 001630 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Classes of Loans by Aging (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesClassesOfLoansByAgingDetails Note 3: Loans and Allowance For Loan Losses: Classes of Loans by Aging (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesClassesOfLoansByAgingTables 163 false false R164.htm 001640 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Financing Receivables NonAccrual Status (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfFinancingReceivablesNonAccrualStatusDetails Note 3: Loans and Allowance For Loan Losses: Schedule of Financing Receivables NonAccrual Status (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfFinancingReceivablesNonAccrualStatusTables 164 false false R165.htm 001650 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Schedule of Loans and Leases Receivable Allowance for Loan Losses (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansAndLeasesReceivableAllowanceForLoanLossesDetails Note 3: Loans and Allowance For Loan Losses: Schedule of Loans and Leases Receivable Allowance for Loan Losses (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesScheduleOfLoansAndLeasesReceivableAllowanceForLoanLossesTables 165 false false R166.htm 001660 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Weighted Average Interest Rate on Loans Receivable (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesWeightedAverageInterestRateOnLoansReceivableDetails Note 3: Loans and Allowance For Loan Losses: Weighted Average Interest Rate on Loans Receivable (Details) Details 166 false false R167.htm 001670 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Loans Serviced for Others (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesLoansServicedForOthersDetails Note 3: Loans and Allowance For Loan Losses: Loans Serviced for Others (Details) Details 167 false false R168.htm 001680 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Impaired Financing Receivables (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesImpairedFinancingReceivablesDetails Note 3: Loans and Allowance For Loan Losses: Impaired Financing Receivables (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesImpairedFinancingReceivablesTables 168 false false R169.htm 001690 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Impaired Loans (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesImpairedLoansDetails Note 3: Loans and Allowance For Loan Losses: Impaired Loans (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesImpairedFinancingReceivablesTables 169 false false R170.htm 001700 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructurings on Financing Receivables (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesTroubledDebtRestructuringsOnFinancingReceivablesDetails Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructurings on Financing Receivables (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesTroubledDebtRestructuringsOnFinancingReceivablesTables 170 false false R171.htm 001710 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Loans Modified in Troubled Debt Restructurings by Segment (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesLoansModifiedInTroubledDebtRestructuringsBySegmentDetails Note 3: Loans and Allowance For Loan Losses: Loans Modified in Troubled Debt Restructurings by Segment (Details) Details 171 false false R172.htm 001720 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructured Loans Returned to Accrual Status (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesTroubledDebtRestructuredLoansReturnedToAccrualStatusDetails Note 3: Loans and Allowance For Loan Losses: Troubled Debt Restructured Loans Returned to Accrual Status (Details) Details 172 false false R173.htm 001730 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Financing Receivable Credit Quality Indicators (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesFinancingReceivableCreditQualityIndicatorsDetails Note 3: Loans and Allowance For Loan Losses: Financing Receivable Credit Quality Indicators (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesFinancingReceivableCreditQualityIndicatorsTables 173 false false R174.htm 001740 - Disclosure - Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure: Schedule of Related Party Transactions (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesRelatedPartyTransactionsDisclosureScheduleOfRelatedPartyTransactionsDetails Note 3: Loans and Allowance For Loan Losses: Related Party Transactions Disclosure: Schedule of Related Party Transactions (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote3LoansAndAllowanceForLoanLossesRelatedPartyTransactionsDisclosureScheduleOfRelatedPartyTransactionsTables 174 false false R175.htm 001750 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy: Business Acquisition, InterBank Assets Acquired and Liabilities Assumed (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsBusinessCombinationsPolicyBusinessAcquisitionInterBankAssetsAcquiredAndLiabilitiesAssumedDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy: Business Acquisition, InterBank Assets Acquired and Liabilities Assumed (Details) Details 175 false false R176.htm 001760 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsBusinessCombinationsPolicyDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Business Combinations Policy (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsBusinessCombinationsPolicyPolicies 176 false false R177.htm 001770 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Business Combination Accretable Yield (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfBusinessCombinationAccretableYieldDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Business Combination Accretable Yield (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfBusinessCombinationAccretableYieldTables 177 false false R178.htm 001780 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Impact of Acquired Loans on Financial Results (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfImpactOfAcquiredLoansOnFinancialResultsDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Impact of Acquired Loans on Financial Results (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfImpactOfAcquiredLoansOnFinancialResultsTables 178 false false R179.htm 001790 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetPolicyDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetRollForwardTables 179 false false R180.htm 001800 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Roll Forward (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetRollForwardDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Roll Forward (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetRollForwardTables 180 false false R181.htm 001810 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy: FDIC Indemnification Asset Roll Forward (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetPolicyFDICIndemnificationAssetRollForwardDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: FDIC Indemnification Asset Policy: FDIC Indemnification Asset Roll Forward (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsFDICIndemnificationAssetPolicyFDICIndemnificationAssetRollForwardTables 181 false false R182.htm 001820 - Disclosure - Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Changes in Accretable Yield for Acquired Loan Pools (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfChangesInAccretableYieldForAcquiredLoanPoolsDetails Note 4: Acquired Loans, Loss Sharing Agreements and FDIC Indemnification Assets: Schedule of Changes in Accretable Yield for Acquired Loan Pools (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote4AcquiredLoansLossSharingAgreementsAndFDICIndemnificationAssetsScheduleOfChangesInAccretableYieldForAcquiredLoanPoolsTables 182 false false R183.htm 001830 - Disclosure - Note 5: Other Real Estate Owned: Schedule of major classifications of other real estate owned (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfMajorClassificationsOfOtherRealEstateOwnedDetails Note 5: Other Real Estate Owned: Schedule of major classifications of other real estate owned (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfMajorClassificationsOfOtherRealEstateOwnedTables 183 false false R184.htm 001840 - Disclosure - Note 5: Other Real Estate Owned: Foreclosures in Process (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedForeclosuresInProcessDetails Note 5: Other Real Estate Owned: Foreclosures in Process (Details) Details 184 false false R185.htm 001850 - Disclosure - Note 5: Other Real Estate Owned: Schedule of expenses applicable to other real estate owned (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfExpensesApplicableToOtherRealEstateOwnedDetails Note 5: Other Real Estate Owned: Schedule of expenses applicable to other real estate owned (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote5OtherRealEstateOwnedScheduleOfExpensesApplicableToOtherRealEstateOwnedTables 185 false false R186.htm 001860 - Disclosure - Note 6: Premises and Equipment: Property, Plant and Equipment (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote6PremisesAndEquipmentPropertyPlantAndEquipmentDetails Note 6: Premises and Equipment: Property, Plant and Equipment (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote6PremisesAndEquipmentPropertyPlantAndEquipmentTables 186 false false R187.htm 001870 - Disclosure - Note 7: Investments in Limited Partnerships: Investments in Affordable Housing Partnerships Policy (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInAffordableHousingPartnershipsPolicyDetails Note 7: Investments in Limited Partnerships: Investments in Affordable Housing Partnerships Policy (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInAffordableHousingPartnershipsPolicyPolicies 187 false false R188.htm 001880 - Disclosure - Note 7: Investments in Limited Partnerships: Investments in Community Development Entities Policy (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInCommunityDevelopmentEntitiesPolicyDetails Note 7: Investments in Limited Partnerships: Investments in Community Development Entities Policy (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote7InvestmentsInLimitedPartnershipsInvestmentsInCommunityDevelopmentEntitiesPolicyPolicies 188 false false R189.htm 001890 - Disclosure - Note 8: Deposits: Schedule of Deposit Liabilities (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfDepositLiabilitiesDetails Note 8: Deposits: Schedule of Deposit Liabilities (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfDepositLiabilitiesTables 189 false false R190.htm 001900 - Disclosure - Note 8: Deposits: Weighted Average Interest Rate on Certificates of Deposit (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsWeightedAverageInterestRateOnCertificatesOfDepositDetails Note 8: Deposits: Weighted Average Interest Rate on Certificates of Deposit (Details) Details 190 false false R191.htm 001910 - Disclosure - Note 8: Deposits: Originated Certificates of Deposit and Brokered Deposits (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsOriginatedCertificatesOfDepositAndBrokeredDepositsDetails Note 8: Deposits: Originated Certificates of Deposit and Brokered Deposits (Details) Details 191 false false R192.htm 001920 - Disclosure - Note 8: Deposits: Maturities of certificates of deposit (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsMaturitiesOfCertificatesOfDepositDetails Note 8: Deposits: Maturities of certificates of deposit (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsMaturitiesOfCertificatesOfDepositTables 192 false false R193.htm 001930 - Disclosure - Note 8: Deposits: Schedule of Interest Expense on Deposit Liabilities (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfInterestExpenseOnDepositLiabilitiesDetails Note 8: Deposits: Schedule of Interest Expense on Deposit Liabilities (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote8DepositsScheduleOfInterestExpenseOnDepositLiabilitiesTables 193 false false R194.htm 001940 - Disclosure - Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank, Advances (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote9AdvancesFromFederalHomeLoanBankFederalHomeLoanBankAdvancesDetails Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank, Advances (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote9AdvancesFromFederalHomeLoanBankFederalHomeLoanBankAdvancesTables 194 false false R195.htm 001950 - Disclosure - Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank Advances Pledged (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote9AdvancesFromFederalHomeLoanBankFederalHomeLoanBankAdvancesPledgedDetails Note 9: Advances From Federal Home Loan Bank: Federal Home Loan Bank Advances Pledged (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote9AdvancesFromFederalHomeLoanBankFederalHomeLoanBankAdvancesTables 195 false false R196.htm 001960 - Disclosure - Note 10: Short-term Borrowings: Schedule of Short-term Debt (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfShortTermDebtDetails Note 10: Short-term Borrowings: Schedule of Short-term Debt (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfShortTermDebtTables 196 false false R197.htm 001970 - Disclosure - Note 10: Short-term Borrowings: Short Term Borrowings (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsShortTermBorrowingsDetails Note 10: Short-term Borrowings: Short Term Borrowings (Details) Details 197 false false R198.htm 001980 - Disclosure - Note 10: Short-term Borrowings: Schedule of Repurchase Agreements (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfRepurchaseAgreementsDetails Note 10: Short-term Borrowings: Schedule of Repurchase Agreements (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote10ShortTermBorrowingsScheduleOfRepurchaseAgreementsTables 198 false false R199.htm 001990 - Disclosure - Note 11: Federal Reserve Bank Borrowings (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote11FederalReserveBankBorrowingsDetails Note 11: Federal Reserve Bank Borrowings (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote11FederalReserveBankBorrowings 199 false false R200.htm 002000 - Disclosure - Note 12: Subordinated Debentures Issued To Capital Trusts: Schedule of Subordinated Debentures Issued to Capital Trusts (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote12SubordinatedDebenturesIssuedToCapitalTrustsScheduleOfSubordinatedDebenturesIssuedToCapitalTrustsDetails Note 12: Subordinated Debentures Issued To Capital Trusts: Schedule of Subordinated Debentures Issued to Capital Trusts (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote12SubordinatedDebenturesIssuedToCapitalTrustsScheduleOfSubordinatedDebenturesIssuedToCapitalTrustsTables 200 false false R201.htm 002010 - Disclosure - Note 13: Subordinated Notes: Schedule of Subordinated Borrowing (Details) Notes http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote13SubordinatedNotesScheduleOfSubordinatedBorrowingDetails Note 13: Subordinated Notes: Schedule of Subordinated Borrowing (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote13SubordinatedNotesScheduleOfSubordinatedBorrowingTables 201 false false R202.htm 002020 - Disclosure - Note 14: Income Taxes: Schedule of Components of Income Tax Expense (Benefit) (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseBenefitDetails Note 14: Income Taxes: Schedule of Components of Income Tax Expense (Benefit) (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseBenefitTables 202 false false R203.htm 002030 - Disclosure - Note 14: Income Taxes: Schedule of Deferred Tax Assets and Liabilities (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails Note 14: Income Taxes: Schedule of Deferred Tax Assets and Liabilities (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesTables 203 false false R204.htm 002040 - Disclosure - Note 14: Income Taxes: Schedule of Effective Income Tax Rate Reconciliation (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetails Note 14: Income Taxes: Schedule of Effective Income Tax Rate Reconciliation (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote14IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationTables 204 false false R205.htm 002050 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets Measured on Recurring Basis (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsMeasuredOnRecurringBasisDetails Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets Measured on Recurring Basis (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsMeasuredOnRecurringBasisTables 205 false false R206.htm 002060 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets and Liabilities Measured on Nonrecurring Basis (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisDetails Note 15: Disclosures About Fair Value of Financial Instruments: Fair Value, Assets and Liabilities Measured on Nonrecurring Basis (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsFairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisTables 206 false false R207.htm 002070 - Disclosure - Note 15: Disclosures About Fair Value of Financial Instruments: Schedule Of Financial Instruments Fair Value (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfFinancialInstrumentsFairValueDetails Note 15: Disclosures About Fair Value of Financial Instruments: Schedule Of Financial Instruments Fair Value (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote15DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfFinancialInstrumentsFairValueTables 207 false false R208.htm 002080 - Disclosure - Note 16: Operating Leases: Schedule of Future Minimum Rental Payments for Operating Leases (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote16OperatingLeasesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesDetails Note 16: Operating Leases: Schedule of Future Minimum Rental Payments for Operating Leases (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote16OperatingLeasesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTables 208 false false R209.htm 002090 - Disclosure - Note 16: Operating Leases: Rental Expense (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote16OperatingLeasesRentalExpenseDetails Note 16: Operating Leases: Rental Expense (Details) Details 209 false false R210.htm 002100 - Disclosure - Note 17: Derivatives and Hedging Activities: Nondesignated Hedges (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesNondesignatedHedgesDetails Note 17: Derivatives and Hedging Activities: Nondesignated Hedges (Details) Details 210 false false R211.htm 002110 - Disclosure - Note 17: Derivatives and Hedging Activities: Derivative Instruments, Gain (Loss) (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesDerivativeInstrumentsGainLossDetails Note 17: Derivatives and Hedging Activities: Derivative Instruments, Gain (Loss) (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesDerivativeInstrumentsGainLossTables 211 false false R212.htm 002120 - Disclosure - Note 17: Derivatives and Hedging Activities: Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossDetails Note 17: Derivatives and Hedging Activities: Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote17DerivativesAndHedgingActivitiesScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTables 212 false false R213.htm 002130 - Disclosure - Note 18: Commitments and Credit Risk: Mortgage Loans in Process of Origination (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRiskMortgageLoansInProcessOfOriginationDetails Note 18: Commitments and Credit Risk: Mortgage Loans in Process of Origination (Details) Details 213 false false R214.htm 002140 - Disclosure - Note 18: Commitments and Credit Risk: Letters of Credit (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRiskLettersOfCreditDetails Note 18: Commitments and Credit Risk: Letters of Credit (Details) Details 214 false false R215.htm 002150 - Disclosure - Note 18: Commitments and Credit Risk: Purchased Letters of Credit (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRiskPurchasedLettersOfCreditDetails Note 18: Commitments and Credit Risk: Purchased Letters of Credit (Details) Details 215 false false R216.htm 002160 - Disclosure - Note 18: Commitments and Credit Risk: Lines of Credit (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRiskLinesOfCreditDetails Note 18: Commitments and Credit Risk: Lines of Credit (Details) Details 216 false false R217.htm 002170 - Disclosure - Note 18: Commitments and Credit Risk: Credit Risk -- Secured Loans (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote18CommitmentsAndCreditRiskCreditRiskSecuredLoansDetails Note 18: Commitments and Credit Risk: Credit Risk -- Secured Loans (Details) Details 217 false false R218.htm 002180 - Disclosure - Note 19: Additional Cash Flow Information: Schedule of Cash Flow, Supplemental Disclosures (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote19AdditionalCashFlowInformationScheduleOfCashFlowSupplementalDisclosuresDetails Note 19: Additional Cash Flow Information: Schedule of Cash Flow, Supplemental Disclosures (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote19AdditionalCashFlowInformationScheduleOfCashFlowSupplementalDisclosuresTables 218 false false R219.htm 002190 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Stock Options, Activity (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationStockOptionsActivityDetails Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Stock Options, Activity (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationStockOptionsActivityTables 219 false false R220.htm 002200 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Fair Value Option Pricing Model Assumptions (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfFairValueOptionPricingModelAssumptionsDetails Note 21: Stock Compensation Plans: Schedule of Fair Value Option Pricing Model Assumptions (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfFairValueOptionPricingModelAssumptionsTables 220 false false R221.htm 002210 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Activity (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationActivityDetails Note 21: Stock Compensation Plans: Schedule of Share-based Compensation, Activity (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfShareBasedCompensationStockOptionsActivityTables 221 false false R222.htm 002220 - Disclosure - Note 21: Stock Compensation Plans: Schedule of Nonvested Share Activity (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfNonvestedShareActivityDetails Note 21: Stock Compensation Plans: Schedule of Nonvested Share Activity (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansScheduleOfNonvestedShareActivityTables 222 false false R223.htm 002230 - Disclosure - Note 21: Stock Compensation Plans: Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableDetails Note 21: Stock Compensation Plans: Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote21StockCompensationPlansShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableTables 223 false false R224.htm 002240 - Disclosure - Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsInAccumulatedOtherComprehensiveIncomeLossToBeRecognizedOverNextFiscalYearDetails Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsInAccumulatedOtherComprehensiveIncomeLossToBeRecognizedOverNextFiscalYearTables 224 false false R225.htm 002250 - Disclosure - Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsReclassifiedFromAccumulatedOtherComprehensiveIncomeDetails Note 23: Accumulated Other Comprehensive Income: Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote23AccumulatedOtherComprehensiveIncomeScheduleOfAmountsReclassifiedFromAccumulatedOtherComprehensiveIncomeTables 225 false false R226.htm 002260 - Disclosure - Note 24: Regulatory Matters: Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote24RegulatoryMattersScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsDetails Note 24: Regulatory Matters: Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote24RegulatoryMattersScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTables 226 false false R227.htm 002270 - Disclosure - Note 26: Summary of Unaudited Quarterly Operating Results: Schedule of Quarterly Financial Information (Details) Sheet http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote26SummaryOfUnauditedQuarterlyOperatingResultsScheduleOfQuarterlyFinancialInformationDetails Note 26: Summary of Unaudited Quarterly Operating Results: Schedule of Quarterly Financial Information (Details) Details http://www.greatsouthernbank.com/20171231/role/idr_DisclosureNote26SummaryOfUnauditedQuarterlyOperatingResultsScheduleOfQuarterlyFinancialInformationTables 227 false false R228.htm 002280 - Disclosure - Note 27: Condensed Parent Company Statements: Condensed Balance Sheet -- Great Southern Bancorp, Inc. 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