Fair value changes in the contingent put option..

No definition available.

Name:	meg_FairValueChangesInContingentPutOption
Namespace Prefix:	meg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of accumulated dividends payable in common stock upon IPO.

+ References

No definition available.

+ Details

Name:	meg_PercentageOfAccumulatedDividendsPayableInCommonStockUponIPO
Namespace Prefix:	meg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of dividend payable in cash.

+ References

No definition available.

+ Details

Name:	meg_PercentageOfDividendPayableInCash
Namespace Prefix:	meg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of dividends accrued.

+ References

No definition available.

+ Details

Name:	meg_PercentageOfDividendsAccrued
Namespace Prefix:	meg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of increase in accrued dividend.

+ References

No definition available.

+ Details

Name:	meg_PercentageOfIncreaseInAccruedDividend
Namespace Prefix:	meg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Temporary equity covenant description.

+ References

No definition available.

+ Details

Name:	meg_TemporaryEquityCovenantDescription
Namespace Prefix:	meg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Temporary equity maturity month and year.

+ References

No definition available.

+ Details

Name:	meg_TemporaryEquityMaturityMonthAndYear
Namespace Prefix:	meg_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Temporary equity penalty term.

+ References

No definition available.

+ Details

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

- Definition

Temporary equity penalty term upon full exercise of warrant.

+ References

No definition available.

+ Details

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

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate amount of redemption requirements for each class or type of redeemable stock classified as temporary equity for each of the five years following the latest balance sheet date. The redemption requirement does not constitute an unconditional obligation that will be settled in a variable number of shares constituting a monetary value predominantly indexed to (a) a fixed monetary amount known at inception, (b) an amount inversely correlated with the residual value of the entity, or (c) an amount determined by reference to something other than the fair value of issuer's stock. Does not include mandatorily redeemable stock. The exception is if redemption is required upon liquidation or termination of the reporting entity.

+ References

No definition available.

+ Details

Name:	us-gaap_TemporaryEquityAggregateAmountOfRedemptionRequirement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

- Definition

The per share liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References

No definition available.

+ Details

Name:	us-gaap_TemporaryEquityLiquidationPreferencePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Per share amount of par value or stated value of stock classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65877616&loc=d3e177068-122764

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (27)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_TemporaryEquityParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27)(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_TemporaryEquitySharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_StatementClassOfStockAxis=meg_RedeemableSeriesAOnePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Redeemable Series A-1 Preferred Stock - Additional Information (Details) - USD ($)		3 Months Ended	6 Months Ended
	Apr. 13, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Oct. 19, 2018
Temporary Equity [Line Items]
Share price		$ 31.60	$ 38.23	$ 31.60
Percentage of dividends paid in cash	14.20%
Redeemable Series A-1 Preferred Stock
Temporary Equity [Line Items]
Temporary equity, shares issued					12,000
Temporary equity, par value per share					$ 0.0001
Warrants to purchase common stock					534,240
Temporary equity, liquidation preference per share					$ 10,000.00
Temporary equity, maturity month and year	2024-10
Temporary equity, penalty term	3 years
Temporary equity, penalty term upon full exercise of warrant	2 years
Percentage of increase in accrued dividend	1.00%
Temporary equity, covenant description			The Redeemable Series A-1 Preferred Stock contained restrictive covenants. Prior to its redemption, the Company was subject to a consolidated total leverage ratio (including the outstanding principal and accrued dividend on the Redeemable Series A-1 Preferred Stock) limit of less than 10.0 times as of the end of any fiscal quarter ending until maturity.
Percentage of dividends paid in cash			15.00%
Percentage of dividends accrued			14.20%
Fair value changes in the contingent put option		$ (22,600,000)		$ 7,000,000.0
Redeemable Series A-1 Preferred Stock \| Maximum
Temporary Equity [Line Items]
Temporary equity, aggregate amount of redemption requirement	$ 50,000,000.0
Percentage of accumulated dividends payable in common stock upon IPO	50.00%
Share price	$ 31.60
Percentage of dividend payable in cash	15.00%
Redeemable Series A-1 Preferred Stock \| Minimum
Temporary Equity [Line Items]
Percentage of dividend payable in cash	9.00%