Name:	gty_AssetRetirementObligationsRemovedFromBalanceSheet
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Leases.

No definition available.

Name:	gty_LeasesLineItems
Namespace Prefix:	gty_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of net asset retirement costs related to underground storage tanks removed from the balance sheet in conjunction with a transfer of related obligations to the lessee.

No definition available.

Name:	gty_NetAssetRetirementCostsRemoved
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Number of leased properties as single unit triple-net leases.

No definition available.

Name:	gty_NumberOfLeasedPropertiesAsSingleUnitTripleNetLeases
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Number of leased properties subject to long-term triple-net leases.

No definition available.

Name:	gty_NumberOfLeasedPropertiesSubjectToLongTermTripleNetLeases
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Number of long-term triple-net leases in portfolios.

No definition available.

Name:	gty_NumberOfLongTermTripleNetLeasesInPortfolios
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of properties previously leased to the tenant.

No definition available.

Name:	gty_NumberOfPropertiesPreviouslyLeased
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Number of properties under redevelopment.

No definition available.

Name:	gty_NumberOfPropertiesUnderRedevelopment
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Number of properties vacant.

No definition available.

Name:	gty_NumberOfPropertiesVacant
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of years in the initial term under unitary triple-net lease agreements.

No definition available.

Name:	gty_PeriodOfInitialTermUnderUnitaryTripleNetLeaseAgreements
Namespace Prefix:	gty_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The number of years in the successive renewal term under unitary triple-net lease agreements.

No definition available.

Name:	gty_PeriodOfSuccessiveRenewalTermsUnderUnitaryTripleNetLeaseAgreements
Namespace Prefix:	gty_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Weighted average remaining lease term, excluding renewal options, for the properties previously leased to marketing.

No definition available.

Name:	gty_WeightedAverageRemainingLeaseTermExcludingRenewalOptionsForThePropertiesPreviouslyLeasedToMarketing
Namespace Prefix:	gty_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Amount of accumulated amortization of deferred initial direct cost for lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 25
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479341/842-30-25-10

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

Amount of excess of rental payment required by lease over rental income recognized.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(26)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 25
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479341/842-30-25-11