The period of time during which failure to follow standard mining industry practices results in a change of control.

No definition available.

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

- Definition

The amount which the reporting entity's subsidiary is required to fund the return of capital contributions previously made. The return of contributions is required because the project did not achieve the specified date for commencement of commercial production.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of reduction of the Return of Contribution owed by Nevada Moly to POS-Minerals on principal payments made for equipment.

+ References

No definition available.

+ Details

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

- Definition

The amount of capital contributions previously made by POS-Minerals which the reporting entity's subsidiary is required. The return of contributions is required because the project did not achieve the specified date for commencement of commercial production.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of remaining capital contributions due to POS-Minerals.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow for acquisition of machinery and equipment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

+ Details

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

- Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_CoVenturerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contingently Redeemable Noncontrolling Interest ("CRNCI") (Details) - Nevada Moly LLC - POS-Minerals Corporation - USD ($) $ in Millions		1 Months Ended				3 Months Ended
	Jan. 01, 2015	Apr. 30, 2016	Apr. 30, 2015	Mar. 31, 2015	Aug. 31, 2013	Mar. 31, 2017
Consecutive months failure to follow standard mining practices						12 months
Obligation to fund return of capital by Nevada Moly to POS-Minerals	$ 36.0				$ 2.9
Remaining amount of capital contribution due to POS Minerals						$ 33.6
Reduction in obligation						$ 2.4
Percentage of reduction on principal payments						20.00%
Milling equipment
Percentage of reduction on principal payments						20.00%
Principal payment made for equipment		$ 1.2		$ 8.4
Electrical transformer
Principal payment made for equipment			$ 2.2