Name:	gnrt_AggregatePrincipalAmountOfOtherDebtUndergoingChangeOfControlThatTriggersChangeOfControlToDebtFacility
Namespace Prefix:	gnrt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the number of periodic or installment payments required under the terms of borrowing.

No definition available.

Name:	gnrt_DebtInstrumentNumberOfPeriodicPayments
Namespace Prefix:	gnrt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the cap on dividends paid as a percentage of consolidated net income as stipulated by debt covenants.

No definition available.

Name:	gnrt_DividendCapAsPercentageOfConsolidatedNetIncome
Namespace Prefix:	gnrt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Number of newbuilding-owning subsidiaries acquired by the Company in the merger

No definition available.

Name:	gnrt_NumberOfNewbuildingOwningSubsidiaries
Namespace Prefix:	gnrt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Description of the frequency of periodic payments (monthly, quarterly, annual).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

Incremental percentage increase (decrease) in the stated rate on a debt instrument.

No definition available.

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

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

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

Name:	us-gaap_LongtermDebtTypeAxis=gnrt_CreditFacility508MillionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=gnrt_CreditFacility273MillionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: