Name:	gmo_AccruedRoyaltiesNonCurrent
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the amount of annual advance royalty payment.

No definition available.

Name:	gmo_AnnualAdvanceRoyaltyPayment
Namespace Prefix:	gmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the period for annual advance royalty payment.

No definition available.

Name:	gmo_AnnualAdvanceRoyaltyPaymentPeriod
Namespace Prefix:	gmo_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the average gross value per pound.

No definition available.

Name:	gmo_AverageGrossValuePerPound
Namespace Prefix:	gmo_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	duration

Cumulative amount paid for Construction Royalty Fee.

No definition available.

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

The minimum annual advance royalty payment required under specified conditions.

No definition available.

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

Period of time after notification before termination of lease is effective.

No definition available.

Name:	gmo_LesseeLeasingArrangementsOperatingLeasesRenewalNoticePeriod
Namespace Prefix:	gmo_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the maximum number of days for receipt of notice.

No definition available.

Name:	gmo_MaximumPeriodForReceiptOfNoticeOfDefault
Namespace Prefix:	gmo_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the maximum number of days for receipt of notice of default in non-payment obligation

No definition available.

Name:	gmo_MaximumPeriodForReceiptOfNoticeOfDefaultInNonPaymentObligation
Namespace Prefix:	gmo_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the molybdenum price per pound.

No definition available.

Name:	gmo_MolybdenumPrice
Namespace Prefix:	gmo_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	duration

Represents the number of installments of royalty payments.

No definition available.

Name:	gmo_NumberOfInstallments
Namespace Prefix:	gmo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The percentage of cash payment of total gross payments received from the purchaser of ores mined/removed/sold from property net of certain deductions.

No definition available.

Name:	gmo_PercentageOfCashPaymentOfTotalGrossPaymentsReceivedFromPurchaserNetOfDeductions
Namespace Prefix:	gmo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the period of commercial production.

No definition available.

Name:	gmo_PeriodOfCommercialProduction
Namespace Prefix:	gmo_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the production royalty as percentage of net returns.

No definition available.

Name:	gmo_ProductionRoyaltyAsPercentageOfNetReturns
Namespace Prefix:	gmo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Royalty Advance Percentage Of Production Royalties.

No definition available.

Name:	gmo_RoyaltyAdvancePercentageOfProductionRoyalties
Namespace Prefix:	gmo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The royalty advance percentage required by long-term Lessor.

No definition available.

Name:	gmo_RoyaltyAdvanceRequiredByLongtermLease
Namespace Prefix:	gmo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the threshold limit for production royalty payment.

No definition available.

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

Carrying value as of the balance sheet date of obligations incurred through that date and payable for royalties.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

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.

No definition available.

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

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

The amount of cash paid for royalties during the current period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585

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

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

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

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

Name:	srt_ProductOrServiceAxis=gmo_OtherNonMolyMineralsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementScenarioAxis=gmo_AverageGrossValueLessThanOrEqualTo2.00PerPoundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ProductOrServiceAxis=gmo_ZincMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementScenarioAxis=gmo_AverageGrossValueBetween2.01And2.49PerPoundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementScenarioAxis=gmo_AverageGrossValueGreaterThan2.50PerPoundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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