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

For an unclassified balance sheet, the accumulated amortization, as of the reporting date, which represents the periodic charge to earnings of initial direct costs which have been deferred and are being allocated over the lease term in proportion to the recognition of rental income.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 16
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481178/840-20-25-16

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 35
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481123/840-20-35-2

Reference 3: 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://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481178/840-20-25-1

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