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Net Income (Loss) Attributable to Parent Basic Earnings (Loss) Per Common Share of SEACOR Marine Holdings Inc. Earnings Per Share, Basic Diluted Earnings (Loss) Per Common Share of SEACOR Marine Holdings Inc. 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[Member] Dynamic Offshore Drilling Ltd [Member] Dynamic Offshore Drilling Ltd. [Member] Sea Cat Crewzer [Member] Sea Cat Crewzer [Member] Sea cat crewzer. 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[Member] SEACOR Holdings Inc. [Member] SEACOR Holdings Inc. [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Employee Stock [Member] Employee Stock [Member] Restricted Stock [Member] Restricted Stock [Member] Employee Stock Option [Member] Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Common stock authorized for grant under the Share Incentive Plans Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Adjustments to Additional Paid in Capital, Other Adjustments to Additional Paid in Capital, Other Stock Issued During Period, Shares, Restricted Stock Award, Gross Stock Issued During Period, Shares, Restricted Stock Award, Gross Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date Restricted stock and restricted stock units vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Additional compensation expense Allocated Share-based Compensation Expense Unrecognized compensation costs Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Compensation costs expected to be recognized in 2018 Compensation Costs Expected to be Recognized in the Next Fiscal Year Compensation costs expected to be recognized in the next fiscal year. Compensation costs expected to be recognized in 2019 Compensation Costs Expected to be Recognized in Two Years Compensation costs expected to be recognized in two years. 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Subsidiary Convertible Senior Notes Derivative Instruments and Hedges, Liabilities, Noncurrent Marketable securities Trading Securities Statement of Stockholders' Equity [Abstract] Statement, Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock [Member] Common Stock [Member] Additional Paid-In Capital [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Retained Earnings [Member] Accumulated Other Comprehensive Loss [Member] AOCI Attributable to Parent [Member] Non-Controlling Interests In Subsidiaries [Member] Noncontrolling Interest [Member] Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Formation of SEACOR Marine Holdings Inc. Proceeds from Contributions from Parent Financial support received upon issuance of convertible senior notes, net of tax Distributions to SEACOR Holdings: Distributed Earnings [Abstract] Cash distributions Cash Dividends Paid to Parent Company by Consolidated Subsidiaries Dividends paid to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Issuance of common stock: Increase (Decrease) in Stockholders' Equity [Roll Forward] Director stock awards Stock Issued During Period, Value, Issued for Services Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Purchase of subsidiary shares from noncontrolling interests, net of tax Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Comprehensive income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Net Loss attributable to SEACOR Marine Holdings Inc. 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Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Restricted stock awards granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Stock Option, Outstanding as of December 31, Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Total Options, Granted, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Stock Options, Exercised, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Stock Options, Forfeited, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Stock Options, Expired, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period Major Customers And Segment Information Segment Reporting Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Interest Expense [Member] Interest Expense [Member] Equity Method Investments [Member] Equity Method Investments [Member] Foreign currency translation gains (losses), net Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax Reclassification of foreign currency translation losses to foreign currency losses, net Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax Reclassification of derivative losses on cash flow hedges Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax Other Comprehensive Income (Loss), before Tax Other Comprehensive Income (Loss), before Tax Income tax (expense) benefit Other Comprehensive Income (Loss), Tax Other Comprehensive Loss, Net of Tax Comprehensive Loss Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive Loss attributable to Noncontrolling Interests in Subsidiaries Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive Loss attributable to SEACOR Marine Holdings Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Statement of Financial Position [Abstract] Trade receivables, allowance for doubtful accounts Allowance for Doubtful Accounts Receivable, Current Common Stock, Par or Stated Value Per Share Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Treasury stock, shares Treasury Stock, Shares Preferred stock, par value Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] C-Lift [Member] C-Lift [Member] C-Lift [Member] Tranche A [Member] Tranche A [Member] Tranche A [Member] Tranche B [Member] Tranche B [Member] Tranche B [Member] Sea-Cat Crewzer III [Member] Sea-Cat Crewzer III [Member] Sea-Cat Crewzer III [Member] BNDES [Member] BNDES [Member] BNDES [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt instrument, stated percentage Convertible Debt Convertible Debt Debt Instrument, Unamortized Discount Debt Instrument, Unamortized Discount Debt Issuance Costs, Gross Debt Issuance Costs, Gross Aggregate principal amount Individual Bond, Face Value Individual Bond, Face Value Individual Bond, Face Value Debt Instrument, Convertible, Conversion Ratio Debt Instrument, Convertible, Conversion Ratio Convertible Securities Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities Bond Redemption Percentage Bond Redemption Percentage Bond Redemption Percentage Payments of Debt Issuance Costs Payments of Debt Issuance Costs Debt Instrument, Final Baloon Payment Debt Instrument, Final Baloon Payment The amount of the final payment due on a debt instrument at maturity. Proceeds from issuance of long-term debt, net of offering costs Proceeds from Issuance of Debt Debt Instrument, Interest Rate, Effective Percentage Debt Instrument, Interest Rate, Effective Percentage Embedded Derivative, Fair Value of Embedded Derivative Liability Embedded Derivative, Fair Value of Embedded Derivative Liability Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Repayments of Long-term Debt Letters of credit outstanding amount Letters of Credit Outstanding, Amount Nature Of Operations And Accounting Policies Business Description and Accounting Policies [Text Block] Commitments and Contingencies [Table] Commitments and Contingencies [Table] Commitments and Contingencies [Table] Wind Farm Utility Vessel [Member] Wind Farm Utility Vessel [Member] Wind Farm Utility Vessel [Member] Commitments and Contingencies [Line Items] Commitments and Contingencies [Line Items] Commitments and Contingencies [Line Items] Unrecorded Unconditional Purchase Obligation, Due within Two Years Unrecorded Unconditional Purchase Obligation, Due within Two Years Unrecorded Unconditional Purchase Obligation Unrecorded Unconditional Purchase Obligation Unrecorded Unconditional Purchase Obligation, Maximum Quantity Unrecorded Unconditional Purchase Obligation, Maximum Quantity Number of equipment leases Property Subject to or Available for Operating Lease, Number of Units Lessee Leasing Arrangements, Operating Leases, Term of Contract Lessee Leasing Arrangements, Operating Leases, Term of Contract Total rental expense for operating leases Operating Leases, Rent Expense, Net Income Taxes Income Tax Disclosure [Text Block] Fair Values Of Derivative Instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Recognized Gains (Losses) On Derivative Instruments Not Designated As Hedging Instruments Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Offshore Support Vessels Standby Safety [Member] Offshore Support Vessels Standby Safety [Member] Offshore Support Vessels Standby Safety Offshore Support Vessels Machinery and Spares [Member] Offshore Support Vessels Machinery and Spares [Member] Offshore Support Vessels Machinery and Spares [Member] Property, Plant and Equipment, Other Types [Member] Property, Plant and Equipment, Other Types [Member] Accumulated Depreciation Property, Plant and Equipment, Other, Accumulated Depreciation Property, Plant and Equipment, Other, Gross Property, Plant and Equipment, Other, Gross Major Customers And Segment Information [Abstract] Major Customers And Segment Information [Abstract] Other Affiliates [Member] Other Affiliates [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Sales Revenue, Net [Member] Sales Revenue, Net [Member] Non-US [Member] Non-US [Member] Investments, at Equity, and Advances to 50% or Less Owned Companies Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Concentration Risk, Percentage Concentration Risk, Percentage Nature of Operations And Accounting Policies [Table] Nature of Operations And Accounting Policies [Table] Nature of Operations And Accounting Policies [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Convertible Debt Securities [Member] Convertible Debt Securities [Member] Nature of Operations and Accounting Policies [Line Items] Nature of Operations and Accounting Policies [Line Items] Nature of operations and accounting policies. Depreciation Depreciation Capitalized interest Capitalized Interest Costs, Including Allowance for Funds Used During Construction Amortization expense Amortization of Intangible Assets Asset Impairment Charges Goodwill, Impairment Loss Goodwill, Impairment Loss Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member] Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member] Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member] Current assets Equity Method Investment, Summarized Financial Information, Current Assets Noncurrent assets Equity Method Investment, Summarized Financial Information, Noncurrent Assets Current liabilities Equity Method Investment, Summarized Financial Information, Current Liabilities Noncurrent liabilities Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities Operating Revenues Equity Method Investment, Summarized Financial Information, Revenue Costs and Expenses: Operating and administrative Equity Method Investment Summarized Financial Information Operating and Administrative Expenses Equity method investment summarized financial information operating and administrative expenses. Costs and Expenses: Depreciation Equity Method Investment Summarized Financial Information Depreciation Equity method investment summarized financial information Depreciation. Total costs and expenses Equity Method Investment Summarized Financial Information Total Costs and Expenses Equity method investment summarized financial information total costs and expenses. Gain (Loss) on Asset Dispositions Equity Method Investment, Summarized Financial Information, Gain (Loss) on Asset Dispositions Equity Method Investment, Summarized Financial Information, Gain (Loss) on Asset Dispositions Operating Income Equity Method Investment, Summarized Financial Information, Income (Loss) from Continuing Operations Net Income (Loss) Equity Method Investment, Summarized Financial Information, Net Income (Loss) Nature Of Operations and Segmentation Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Basis Of Consolidation Consolidation, Policy [Policy Text Block] Use Of Estimates Use of Estimates, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Marketable Securities Marketable Securities, Policy [Policy Text Block] Trade Receivables Receivables, Policy [Policy Text Block] Derivative Instruments Derivatives, Policy [Policy Text Block] Concentrations Of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Inventories Inventory, Policy [Policy Text Block] Property And Equipment Property, Plant and Equipment, Policy [Policy Text Block] Intangible Assets Intangible Assets, Finite-Lived, Policy [Policy Text Block] Impairment Of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Including Intangible Assets, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Business Combinations Business Combinations Policy [Policy Text Block] Deferred Financing Costs Deferred Charges, Policy [Policy Text Block] Self-Insurance Liabilities Self Insurance Reserve [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Deferred Gains Deferred Gains [Policy Text Block] Disclosure of accounting policy for the deferral and amortization of gains on asset sales to 50% or less owned companies and gains on sale and leaseback transactions of significant deferred charges. Foreign Currency Translation And Transactions Foreign Currency Transactions and Translations Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) State Current State and Local Tax Expense (Benefit) Foreign Current Foreign Tax Expense (Benefit) Current Income Tax Expense, Total Current Income Tax Expense (Benefit) Federal Deferred Federal Income Tax Expense (Benefit) State Deferred State and Local Income Tax Expense (Benefit) Foreign Deferred Foreign Income Tax Expense (Benefit) Deferred Income Tax Benefit, Total Deferred Income Tax Expense (Benefit) Income Tax Benefit Income Tax Expense (Benefit) Savings Plans And Multiemployer Pension Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Estimated useful life (in years) Property, Plant and Equipment, Useful Life Total Minimum Payments, 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months Total Minimum Payments, 2019 Operating Leases, Future Minimum Payments, Due in Two Years Total Minimum Payments, 2020 Operating Leases, Future Minimum Payments, Due in Three Years Total Minimum Payments, 2021 Operating Leases, Future Minimum Payments, Due in Four Years Total Minimum Payments, 2022 Operating Leases, Future Minimum Payments, Due in Five Years Derivative [Table] Derivative [Table] Equity Option [Member] Equity Option [Member] Foreign Exchange Forward [Member] Foreign Exchange Forward [Member] Embedded Derivative, Gain on Embedded Derivative Embedded Derivative, Gain on Embedded Derivative Derivative gains (losses), net Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Class of Treasury Stock [Table] Class of Treasury Stock [Table] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Contributions from SEACOR Holdings Distributions to SEACOR Holdings Document And Entity Information [Abstract] Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float Property, Plant and Equipment Impairment or Disposal [Abstract] Acquisitions and Dispositions (Major Equipment Dispositions) [Table] Number of Equipments Removed from Service Number of Equipments Removed from Service Number of equipments removed from service. Cash Flow Supplemental Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Equipment Acquisitions [Abstract] Equipment Acquisitions [Abstract] Number Of Equipments Acquired Number of Equipment Acquired Number of Equipment Acquired Payments to Acquire Property, Plant, and Equipment Payments to Acquire Property, Plant, and Equipment 2018 Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months 2019 2020 Unrecorded Unconditional Purchase Obligation, Due within Three Years Deferred Unrecorded Unconditional Purchase Obligation, Due after Five Years Schedule Of Company's Borrowings Schedule of Long-term Debt Instruments [Table Text Block] Schedule Of Long-Term Debt Maturities Schedule of Maturities of Long-term Debt [Table Text Block] 2018 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four 2022 Long-term Debt, Maturities, Repayments of Principal in Year Five Years subsequent to 2022 Long-term Debt, Maturities, Repayments of Principal after Year Five Long-term Debt, Gross Long-term Debt, Gross Quarterly Financial Information Quarterly Financial Information [Table Text Block] Other Comprehensive Income Location [Axis] Other Comprehensive Income Location [Axis] Other Comprehensive Income Location [Domain] Other Comprehensive Income Location [Domain] Deferred Income Tax Charge [Member] Deferred Income Tax Charge [Member] Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Loss, before Tax Other Comprehensive Income (Loss), Tax ASSETS Assets [Abstract] Current Assets: Assets, Current [Abstract] Cash and cash equivalents Restricted cash Restricted Cash and Cash Equivalents, Current Marketable securities Marketable Securities, Current Receivables: Receivables [Abstract] Trade, net of allowance for doubtful accounts of $4,039 and $5,359 in 2017 and 2016, respectively Accounts Receivable, Net, Current Due from SEACOR Holdings Due from Affiliate, Current Other Other Receivables, Net, Current Inventories Inventory, Net Prepaid expenses and other Prepaid Expense and Other Assets, Current Total current assets Assets, Current Property and Equipment: Property, Plant and Equipment [Abstract] Historical cost Accumulated depreciation Property, Plant and Equipment, Net In Service Construction in progress Construction in Progress, Gross Net property and equipment Property, Plant and Equipment, Net Other Assets Other Assets, Noncurrent Total Assets Assets LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Current Liabilities: Liabilities, Current [Abstract] Current portion of long-term debt Long-term Debt, Current Maturities Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities, Current Due to SEACOR Holdings Due to Affiliate, Current Accrued wages and benefits Employee-related Liabilities, Current Accrued income taxes Accrued Income Taxes, Current Accrued capital, repair and maintenance expenditures Accrued Liabilities, Current Deferred revenues Deferred Revenue, Current Other current liabilities Other Liabilities, Current Total current liabilities Liabilities, Current Long-Term Debt Long-term Debt, Excluding Current Maturities Exchange Option Liability on 3.75% Convertible Senior Notes Deferred Income Taxes Deferred Tax Liabilities, Net, Noncurrent Deferred Gains and Other Liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] SEACOR Holdings Inc. stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock, $.01 par value, 10,000,000 shares authorized; none issued nor outstanding Preferred Stock, Value, Issued Common stock, $.01 par value, 60,000,000 shares authorized; 17,675,356 and 17,671,356 shares issued in 2017 and 2016, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss, net of tax Stockholders' equity attributable to SEACOR Holdings Inc. Stockholders' Equity Attributable to Parent Total equity Liabilities and stockholders' equity, total Liabilities and Equity Derivative Instruments And Hedging Strategies Derivative Instruments and Hedging Activities Disclosure [Text Block] Share Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Noncontrolling Interest Disclosure [Text Block] Noncontrolling Interest Disclosure [Text Block] Disclosure Text Block [Abstract] Property, Plant and Equipment Disclosure [Text Block] Property, Plant and Equipment Disclosure [Text Block] Property, Plant and Equipment [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table Text Block] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Other Offshore Marine Services Joint Ventures [Member] Other Offshore Marine Services Joint Ventures [Member] Other Offshore Marine Services Joint Ventures [Member] Impaired Long-Lived Assets Held and Used by Type [Axis] Impaired Long-Lived Assets Held and Used by Type [Axis] Impaired Long-Lived Assets Held and Used, Asset Name [Domain] Impaired Long-Lived Assets Held and Used, Asset Name [Domain] Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Cumulative undistributed net earnings of 50% or less owned companies accounted for by the equity method included in the Company's consolidated retained earnings Equity Method Investment, Unrealized Intercompany Profit (Loss) Not Eliminated, Amount Partners' Capital Account, Contributions Partners' Capital Account, Contributions Repayments of Secured Debt Repayments of Secured Debt Payments to Acquire Machinery and Equipment Payments to Acquire Machinery and Equipment Repayments of Advances Repayment of Notes Receivable from Related Parties Related party transaction expense Related Party Transaction, Expenses from Transactions with Related Party Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital Payments for Advance to Affiliate Payments for Advance to Affiliate Allocable share of uncalled capital Allocable Share of Uncalled Capital Allocable share of uncalled capital. Guarantee of outstanding charter receivables Guarantee of Outstanding Charter Receivables Guarantee of outstanding charter receivables. Equity Method Investment Summarized Financial Information Total Costs and Expenses Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months Income Statement [Abstract] Costs and Expenses: Costs and Expenses [Abstract] Operating Operating Costs and Expenses Total costs and expenses Costs and Expenses Operating Loss Other Income (Expense): Other Income and Expenses [Abstract] Interest income Investment Income, Interest Interest expense Interest Expense Interest income on advances and notes with SEACOR Holdings, net Interest Income, Related Party SEACOR Holdings management fees Management Fee Expense SEACOR Holdings guarantee fees Costs and Expenses, Related Party Marketable security gains (losses), net Marketable Securities, Gain (Loss) Derivative gains (losses), net Gain (Loss) on Derivative Instruments, Net, Pretax Foreign currency losses, net Foreign Currency Transaction Gain (Loss), before Tax Other, net Other Nonoperating Income (Expense) Nonoperating Income (Expense) Nonoperating Income (Expense) Loss Before Income Tax Benefit and Equity in Earnings (Losses) of 50% or Less Owned Companies Income Tax Benefit: Current Deferred Loss Before Equity in Earnings (Losses) of 50% or Less Owned Companies Income Before Equity in Earnings of 50% or Less Owned Companies Income before equity in earnings of 50% or less owned companies. Net Loss Net Income (Loss) Attributable to Noncontrolling Interests in Subsidiaries Net Loss attributable to SEACOR Marine Holdings Inc. Basic Loss Per Common Share of SEACOR Marine Holdings Inc. Diluted Loss Per Common Share of SEACOR Marine Holdings Inc. Weighted Average Common Shares Outstanding: Weighted Average Common Shares Outstanding Abstract Weighted Average Common Shares Outstanding Abstract Basic Weighted Average Common Shares Outstanding Weighted Average Number of Shares Outstanding, Basic Foreign Exchange [Member] Foreign Exchange [Member] Designated as Hedging Instrument [Member] Designated as Hedging Instrument [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative Asset Derivative Asset, Fair Value, Gross Asset Derivative Liability Derivative Liability, Fair Value, Gross Liability Embedded Derivative, Fair Value of Embedded Derivative Asset Embedded Derivative, Fair Value of Embedded Derivative Asset Long-term Debt, Gross Portion due within one year, net of related debt discount and issuance costs Debt discount included in long-term debt Debt issuance costs included in long-term debt Debt Issuance Costs, Noncurrent, Net Long-term Debt, Excluding Current Maturities Other Restricted Assets [Abstract] Withdrawals Construction Reserve Fund Withdrawals Construction reserve fund withdrawals. Deposits Construction Reserve Fund Deposits Construction reserve fund deposits. Construction Reserve Fund Activity Net Construction Reserve Fund Activity Net Net activity in construction reserve funds during the period. Statement of Cash Flows [Abstract] Cash Flows from Operating Activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile income to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Amortization of deferred gains on sale and leaseback transactions Sale Leaseback Transaction, Current Period Gain Recognized Debt discount and issuance cost amortization, net Amortization of Debt Discount (Premium) Director stock awards Director Stock Awards Director stock awards. Amortization of share awards Share-based Compensation Marketable security (gains) losses, net Purchases of marketable securities Payments for Purchase of Securities, Operating Activities Proceeds from sale of marketable securities Proceeds from Sale of Securities, Operating Activities Cash settlements on derivative transactions, net Payments for (Proceeds from) Derivative Instruments, Operating Activities The net amount of cash paid or received to settle derivatives during the period not designated as hedges. Deferred income tax benefit Other, net Proceeds from Other Operating Activities Equity in (earnings) losses of 50% or less owned companies, net of tax Dividends received from 50% or less owned companies Proceeds from Dividends Received Changes in operating assets and liabilities: Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract] Decrease in receivables Increase (Decrease) in Receivables (Increase) decrease in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Decrease in accounts payable, accrued expenses and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Cash Flows from Investing Activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of property and equipment Cash settlements on derivative transactions, net Payments for (Proceeds from) Hedge, Investing Activities Proceeds from disposition of property and equipment Return of investments and advances of 50% or less owned companies Proceeds from Equity Method Investment, Dividends or Distributions (Issuances of) payments received on third party leases and notes receivable, net Payments for (Proceeds from) Loans and Leases Net (increase) decrease in restricted cash Increase (Decrease) in Restricted Cash Net (increase) decrease in construction reserve funds Payments for (Proceeds from) Other Investing Activities Cash assumed on consolidation of 50% or less owned companies Business acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash Flows from Financing Activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Payments on long-term debt and capital lease obligations Repayments of Debt and Capital Lease Obligations Proceeds from Issuance of long-term debt, net of offering costs Proceeds from Issuance of Long-term Debt Payments on advances and notes with SEACOR Holdings, net Proceeds from Other Equity Distribution of SEACOR Marine restricted stock to Company personnel by SEACOR Holdings Proceeds from (Payments for) Other Financing Activities Distributions to SEACOR Holdings Purchase of subsidiary shares from noncontrolling interests Payments to Acquire Additional Interest in Subsidiaries Dividends paid to noncontrolling interests, net Proceeds from (Payments to) Noncontrolling Interests Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Effects of Exchange Rate Changes on Cash and Cash Equivalents Effect of Exchange Rate on Cash and Cash Equivalents, Continuing Operations Net Increase (Decrease) in Cash and Cash Equivalents Net Cash Provided by (Used in) Continuing Operations Cash and Cash Equivalents, Beginning of Year Cash and Cash Equivalents, End of Year