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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Jun. 30, 2018
--- | --- | ---
Project Unapproved Change Orders and Claims [Line Items] |  |
Unapproved change orders and claims | $ 13.2 | $ 15.0

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- Definition [Line Items] for Power Generation Project Unapproved Change Orders and Claims [Table] + References No definition available. + Details
Name: | mtrx_PowerGenerationProjectUnapprovedChangeOrdersandClaimsLineItems
Namespace Prefix: | mtrx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of cost incurred on construction contract for unapproved change order, claim, or similar item subject to uncertainty. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 910 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6471471&loc=d3e48698-109348 + Details
Name: | us-gaap_UnapprovedChangeOrdersAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant