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Fast Support Vessels [Member] Information pertaining to fast support vessels. smhi_ProceedsFromSaleOfPropertyPlantAndEquipmentIncludingDeposits Proceeds from Sale of Property, Plant, and Equipment, Including Deposits The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale, including deposits. 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Revenues deferred during the period Sea-Cat Crewzer II [Member] Information pertaining to Sea-Cat Crewzer II. us-gaap_DeferredRevenueRevenueRecognized1 Revenues recognized during the period smhi_NumberOfEquipmentOperated Number of Equipment Operated Represents the number of equipment operated. us-gaap_ConvertibleDebt Convertible Debt, Total Other Comprehensive Income (Loss): MexMar [Member] Information pertaining to MexMar. SEACOR Holdings [Member] Information pertaining to SEACOR Holdings. Sea-Cat Crewzer [Member] Information pertaining to Sea-Cat Crewzer. us-gaap_DeferredRevenue Deferred Revenue Balance at beginning of period Balance at end of period Windcat Workboats [Member] Information pertaining to Windcat Workboats. Supply Vessels [Member] Information pertaining to supply vessels. us-gaap_RepaymentsOfLongTermDebt Repayments of Long-term Debt, Total Payments on long-term debt Other Noncontrolling Interests [Member] Information pertaining to other noncontrolling interests. Construction reserve funds Fair value portion of construction reserve funds. Schedule of Noncontrolling Interest [Table Text Block] Tabular disclosure of noncontrolling interest. smhi_AllocableShareOfUncalledCapital Allocable Share of Uncalled Capital Represents the entity's allocable share of uncalled capital. Other Offshore Marine Services Joint Ventures [Member] Information pertaining to other offshore marine services joint ventures. us-gaap_DebtInstrumentUnamortizedDiscount Debt Instrument, Unamortized Discount, Total OSV Partners [Member] Information pertaining to OSV Partners. Dynamic Offshore [Member] Information pertaining to Dynamic Offshore. Accounting Policies [Abstract] us-gaap_PartnersCapitalAccountContributions Partners' Capital Account, Contributions smhi_OtherLaborAndPerformanceGuarantee Other Labor and Performance Guarantee Represents the amount of other labor and performance guarantees. us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption Cumulative Effect of New Accounting Principle in Period of Adoption Impact of adoption of accounting principle Interest Expense [Member] us-gaap_ProceedsFromIssuanceOfLongTermDebt Proceeds from Issuance of Long-term Debt, Total Brazil, Mexico, Central and South America [Member] Information pertaining to Brazil, Mexico, Central and South America. Time Charter [Member] Information pertaining to time charter. Middle East and Asia [Member] Information pertaining to Middle East and Asia. Personnel [Member] Information pertaining to personnel services. Repairs and Maintenance [Member] Information pertaining to repairs and maintenance services. Income Statement Location [Axis] Bareboat Charter [Member] Information pertaining to bareboat charter. Income Statement Location [Domain] Other Marine Services [Member] Information pertaining to other marine services. Fuel, Lubes and Supplies [Member] Information pertaining to fuel, lubes and supplies. Other Direct Costs and Expenses [Member] Information pertaining to other direct costs and expenses. Drydocking [Member] Information pertaining to drydocking services. Insurance and Loss Reserves [Member] Information pertaining to insurance and loss reserves. Leased-in Equipment [Member] Information pertaining leased-in equipment. Noncontrolling interest percent Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners smhi_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsAndNoncontrollingInterestAfterTax Loss Before Equity in Earnings of 50% or Less Owned Companies Amount of income (loss) from continuing operations before income (loss) from equity method investments and income (loss) attributable to noncontrolling interest, but after tax of income (loss) from continuing operations. us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount us-gaap_OperatingLossCarryforwards Operating Loss Carryforwards, Total us-gaap_ProceedsFromLinesOfCredit Proceeds from Lines of Credit, Total Due to SEACOR Holdings smhi_PropertyPlantAndEquipmentExcludingConstructionInProgress Amount after accumulated depreciation, depletion and amortization of physical assets, excluding construction in progress, used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. Construction Reserve Funds Amount of construction reserve funds as of the balance sheet date. 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Falcon Global USA LLC [Member] Information pertaining to Falcon Global USA LLC. us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary Unrecorded Unconditional Purchase Obligation, Due within Two Years us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary Unrecorded Unconditional Purchase Obligation, Due within Three Years smhi_PaymentsForDebtorInPossessionObligations Payments for Debtor-in-possession Obligations Amount of cash outflow for debtor-in-possession obligations. Term Loan [Member] Information pertaining to the term loan. Foreign currency translation gains (losses) Standby Safety Vessels [Member] Information pertaining to standby safety vessels. Carlyle Group [Member] Information pertaining to Carlyle Group. us-gaap_StockholdersEquity us-gaap_PaymentsToAcquireEquityMethodInvestments Investments in and advances to 50% or less owned companies smhi_CapitalCall Capital Call Represents the amount of capital call. SeaCosco Offshore LLC [Member] Information pertaining to SeaCosco Offshore LLC. Class of Stock [Axis] Long-Term Debt Comprehensive Income (Loss) [Table Text Block] Grant DIS [Member] Information pertaining to Grant DIS. Interest Rate Swap [Member] us-gaap_DerivativeFixedInterestRate Derivative, Fixed Interest Rate Foreign Exchange Option [Member] Other