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The Company's domestic net deferred tax liability balance was remeasured at a lower corporate tax rate, which reduced the net deferred tax liability balance. The downward remeasurement was recorded as a benefit to income tax expense. 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The use of this blended rate is stipulated by the Internal Revenue Code in connection with the Tax Cuts and Jobs Act of December 2017, which reduced the federal income tax rate from 35% to 21%. Since the Company has a June 30 fiscal year end, it must use a blend of 21% and 35% for the rest of the current fiscal year. 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Earnings Per Share [Abstract] Earnings Per Share [Abstract] Utility and Power Infrastructure [Member] Utility and Power Infrastructure [Member] Utility and Power Infrastructure. Treasury shares purchased to satisfy tax withholding obligations Other Treasury Share Purchases Other treasury share purchases. Total property, plant and equipment - at cost Property, Plant and Equipment, Gross Disclosure Customer Contracts Additional Information [Abstract] Disclosure Customer Contracts Additional Information [Abstract] Disclosure - Customer Contracts - Additional Information [Abstract] Document Quarterly Report Document Quarterly Report Other assets and liabilities Increase (Decrease) in Other Operating Assets Revenue Revenues Severance costs and other benefits Severance Costs Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Restructuring costs by type [Abstract] Restructuring costs by type [Abstract] Restructuring costs by type [Abstract] Goodwill Goodwill, Gross Total future payments for lease not yet commenced Total future payments for lease not yet commenced Total future payments for lease not yet commenced Revenue, Performance Obligation [Abstract] Revenue, Performance Obligation [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Document Fiscal Period Focus Document Fiscal Period Focus Effective Income Tax Rate Reconciliation, Deduction, Other, Amount Effective Income Tax Rate Reconciliation, Deduction, Other, Amount Effective Income Tax Rate Reconciliation, Percent Effective Income Tax Rate Reconciliation, Percent Net loss Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restricted Cash, Current Restricted Cash, Current Line Of Credit Basis Spread On Adjusted LIBO and CDOR Maximum Line Of Credit Basis Spread On Adjusted LIBO and CDOR Maximum Line Of Credit Basis Spread On Adjusted LIBO and CDOR Maximum Gross revenues Gross revenues Gross revenues before intersegment eliminations Gain on sale of property, plant and equipment Gain (Loss) on Disposition of Property Plant Equipment Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning of Period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, End of Period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Costs and estimated earnings in excess of billings on uncompleted contracts Contract with Customer, Asset, after Allowance for Credit Loss, Current United States UNITED STATES Common stock, par value Common Stock, Par or Stated Value Per Share Current assets: Assets, Current [Abstract] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Finite-Lived Intangible Assets, Gross Finite-Lived Intangible Assets, Gross Leases [Abstract] Leases [Abstract] Entity Central Index Key Entity Central Index Key Finite-Lived Intangible Assets, Remaining Amortization Period Finite-Lived Intangible Assets, Remaining Amortization Period Security Exchange Name Security Exchange Name Project Unapproved Change Orders and Claims [Table] Power Generation Project Unapproved Change Orders and Claims [Table] Power Generation Project Unapproved Change Orders and Claims [Table] Exercise of stock options, shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Diluted Diluted weighted average shares (shares) Weighted Average Number of Shares Outstanding, Diluted Income Tax Disclosure Income Tax Disclosure [Text Block] Current Fiscal Year End Date Current Fiscal Year End Date mtrx:BusinessImprovementPlan [Member] mtrx:BusinessImprovementPlan [Member] Business Improvement Plan Antidilutive Securities Excluded from the Calculation of Diluted EPS Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Finite-Lived Intangible Assets, Amortization Expense, Year Five Finite-Lived Intangible Asset, Expected Amortization, Year Five Text Block [Abstract] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other Restructuring Costs Other Restructuring Costs Baillie Tank Equipment, Ltd. [Member] Baillie Tank Equipment, Ltd. [Member] Baillie Tank Equipment, Ltd. [Member] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Net cash used by investing activities Net Cash Provided by (Used in) Investing Activities Disaggregation of Revenue [Abstract] Disaggregation of Revenue [Abstract] Changes in operating assets and liabilities increasing (decreasing) cash: Increase (Decrease) in Operating Capital [Abstract] Treasury shares sold to Employee Stock Purchase Plan Stock Issued During Period, Value, Employee Stock Purchase Plan Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Restriction of deductibility of certain executive compensation Restriction of deductibility of certain executive compensation Restriction of deductibility of certain executive compensation in excess of $1.0 million. Description of one of the major changes in connection with the Tax Cuts and Jobs Act of December 2017. Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Increase (Decrease) in Income Taxes Receivable Increase (Decrease) in Income Taxes Receivable Total current liabilities Liabilities, Current Class of Stock [Domain] Class of Stock [Domain] Intersegment Eliminations [Member] Intersegment Eliminations [Member] Corporate [Member] Unallocated Corporate Costs [Member] Unallocated Corporate Costs. Construction Contractor, Receivable, Retainage, after Year One Construction Contractor, Receivable, Retainage, after Year One Senior credit facility Senior secured revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Loss Contingencies [Table] Loss Contingencies [Table] Revenue from Contract with Customer Revenue from Contract with Customer, Including Assessed Tax Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Beginning equity balances, as adjusted Beginning equity balances, as adjusted Beginning equity balances as adjusted for the effects of retrospective impacts of the adoption of a new accounting standard. Entity Address, Postal Zip Code Entity Address, Postal Zip Code Land and buildings Buildings and Improvements, Gross Title of 12(b) Security Title of 12(b) Security Proceeds from issuance of common stock under employee stock purchase plan Proceeds from Stock Plans Other current assets Other Assets, Current Statement [Table] Statement [Table] New Accounting Pronouncements, Policy New Accounting Pronouncements, Policy [Policy Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Issuance of deferred shares Adjustments to Additional Paid in Capital, Other Expected Remaining Amortization Expense [Abstract] Expected Remaining Amortization Expense [Abstract] Expected Remaining Amortization Expense [Abstract] Cover [Abstract] Cover [Abstract] Net Carrying Amount Finite-Lived Intangible Assets, Net Finite-Lived Intangible Assets, Net Goodwill Goodwill Net balance at June 30, 2020 Net balance at September 30, 2021 Goodwill Construction in progress Construction in Progress, Gross Operating Loss Carryforwards, Limitations on Use Operating Loss Carryforwards, Limitations on Use Schedule of Goodwill [Table Text Block] Schedule of Goodwill [Table Text Block] Other treasury shares purchases, shares Other Treasury Shares Acquired Other treasury shares acquired. Operating lease expense Operating Lease, Cost Other Information Related to Leases [Table Text Block] Other Information Related to Leases [Table Text Block] Table disclosing operating lease weighted average remaining lease term, weighted average discount rate, and supplemental cash flow disclosures. Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Adjustments to reconcile net loss to net cash used by operating activities: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]