Aggregate amount of equipment orders.

No definition available.

Name:	gmo_AggregateAmountOfEquipmentOrders
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of equipment orders relate to fully fabricated items.

+ References

No definition available.

+ Details

Name:	gmo_AmountOfEquipmentOrdersRelatedToFullyFabricatedItems
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of equipment orders relate to partially fabricated milling equipment and non-refundable deposits on mining equipment.

+ References

No definition available.

+ Details

Name:	gmo_AmountOfEquipmentOrdersRelatedToPartiallyFabricatedMillingEquipmentAndNonRefundableDeposits
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The remaining reserve balance from the initial fund from members.

+ References

No definition available.

+ Details

Name:	gmo_InitialFundFromMembersReserveAccountBalance
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents cash and equivalents whose use in whole or in part is restricted for long-term use by the limited liability corporation.

+ References

No definition available.

+ Details

Name:	gmo_RestrictedCashHeldByLimitedLiabilityCorporation
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis=us-gaap_PurchaseCommitmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=gmo_MiningAndMillingEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=gmo_EurekaMolyLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=gmo_MountHopeProjectMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=gmo_AmerInternationalGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DESCRIPTION OF BUSINESS - Purchase Commitment excluding Long-term Commitment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 09, 2019	Apr. 17, 2015
Cash commitments
Amount committed to be purchased	$ 600
Restricted cash held at EMLLC	3,684	$ 3,388
Purchase Commitment \| Mining and milling equipment \| Eureka Moly LLC
Cash commitments
Aggregate amount of equipment orders	88,000
Amount of equipment orders relate to fully fabricated items	71,700
Amount of equipment orders relate to partially fabricated milling equipment, and non-refundable deposits on mining equipment	16,300
Mt. Hope Project
Cash commitments
Balance of reserve account	3,700	3,400
Restricted cash held at EMLLC	3,700	$ 3,400
Mt. Hope Project \| Eureka Moly LLC
Cash commitments
Aggregate amount of equipment orders	$ 88,000
Senior secured term loan \| Mt. Hope Project \| AMER International Group
Cash commitments
Face amount			$ 700,000	$ 700,000