Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Dec. 31, 2021	Jan. 01, 2021
Lessee Lease Description [Line Items]
Operating lease right-of-use assets	$ 30,129	$ 23,532	$ 24,600
Current operating lease liabilities	8,368	6,888	7,300
Operating lease liabilities, net of current portion	22,128	16,859	17,300
Finance lease right-of-use assets	8,493	8,944	7,200
Current finance lease liabilities	3,477	3,512	2,900
Finance lease liabilities, net of current portion	$ 5,372	$ 5,756	$ 4,600
Minimum
Lessee Lease Description [Line Items]
Lessee operating and finance lease term	1 year
Maximum
Lessee Lease Description [Line Items]
Lessee operating and finance lease term	15 years

Lessee operating and finance lease term of contract.

No definition available.

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Namespace Prefix:	meg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease, classified as noncurrent.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Details

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