Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2020
Project Unapproved Change Orders and Claims [Line Items]
Unapproved change orders and claims	$ 13.0	$ 14.5
Loss Contingencies [Line Items]
Contracts Receivable, Claims and Uncertain Amounts	$ 16.9

[Line Items] for Power Generation Project Unapproved Change Orders and Claims [Table]

No definition available.

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Namespace Prefix:	mtrx_
Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Amount of billed or unbilled claims or other similar items subject to uncertainty concerning their determination or ultimate realization under long-term contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 910
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119991564&loc=SL119991585-234733

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(c)(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- 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

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant