Adjustments to additional paid In capital stock issued issuance costs including underwriters fees.

No definition available.

Name:	gmhi_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCostsIncludingUnderwritersFees
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Adjustments to additional paid in capital, stock issued, underwriter’s fees.

+ References

No definition available.

+ Details

Name:	gmhi_AdjustmentsToAdditionalPaidInCapitalStockIssuedUnderwritersFees
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The maximum amount of dissolution expenses allowed in the event a Business Combination is not completed in accordance with conditions stated.

+ References

No definition available.

+ Details

Name:	gmhi_DissolutionExpensesMaximumAllowed
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of shares the company will redeem if business combination is not completed at specified time period.

+ References

No definition available.

+ Details

Name:	gmhi_PercentageOfRedemptionIfBusinessCombinationNotCompleted
Namespace Prefix:	gmhi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Redemption rights or liquidating distributions with respect to warrants.

+ References

No definition available.

+ Details

Name:	gmhi_RedemptionRightsOrLiquidatingDistributionsWithRespectToWarrants
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Significant accounting policies.

+ References

No definition available.

+ Details

Name:	gmhi_SignificantAccountingPoliciesLineItems
Namespace Prefix:	gmhi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold net tangible assets below which the company will not redeem public shares.

+ References

No definition available.

+ Details

Name:	gmhi_ThresholdNetTangibleAssetsForRedemptionOfPublicShares
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Threshold number of period in which the public shares are to be redeemed if business combination is not completed within the specified period of time.

+ References

No definition available.

+ Details

Name:	gmhi_ThresholdNumberOfPeriodToRedeemPublicSharesIfBusinessCombinationIsNotComplete
Namespace Prefix:	gmhi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold period to complete business combination from closing of public offering.

+ References

No definition available.

+ Details

Name:	gmhi_ThresholdPeriodToCompleteBusinessCombinationFromClosingOfPublicOffering
Namespace Prefix:	gmhi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Working capital.

+ References

No definition available.

+ Details

Name:	gmhi_WorkingCapital
Namespace Prefix:	gmhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of cash, securities, or other assets held by a third-party trustee pursuant to the terms of an agreement which assets are available to be used by beneficiaries to that agreement only within the specific terms thereof and which agreement is expected to terminate more than one year from the balance sheet date (or operating cycle, if longer) at which time the assets held-in-trust will be released or forfeited.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(b))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Name:	us-gaap_AssetsHeldInTrustNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of cash deposited in financial institutions as of the balance sheet date that is insured by the Federal Deposit Insurance Corporation.

+ References

No definition available.

+ Details

Name:	us-gaap_CashFDICInsuredAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise stock options, restrictive stock units (RSUs), convertible preferred stock of an employee stock ownership plan (ESOP), and other dilutive convertible securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

+ Details

Name:	us-gaap_DilutiveSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.21)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

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

- Definition

Number of new stock issued during the period.

+ 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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 4: 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- 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

+ Details

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

- Details

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

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_IPOMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant Accounting Policies - Additional Information (Details) - USD ($)		6 Months Ended
	Feb. 05, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Significant Accounting Policies [Line Items]
Dilutive securities, effect on basic earnings per share		$ 0
Federal depository insurance coverage amount		$ 250,000
Class A common stock subject to possible redemption (in shares)		38,713,476	38,713,476	38,489,273
Redemption percentage if business combination is not completed		100.00%
Investments and cash held in Trust Account		$ 406,397,612	$ 406,434,959
Dissolution expenses, maximum allowed		100,000
Redemption rights or liquidating distributions with respect to warrants		0
Current liabilities		300,543	1,355,865
Working capital		818,353	$ 145,774
Maximum
Significant Accounting Policies [Line Items]
Threshold net tangible assets		$ 5,000,001
Number of months to complete business combination		24 months
Number of days to redeem the shares if Business combination is not completed		10 days
IPO
Significant Accounting Policies [Line Items]
Offering costs including underwriter's fees	$ 22,865,105
Underwriter's fees	$ 22,000,000
Sale of common stock (in shares)	40,000,000