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Description of Business - Additional Information (Detail) | Jun. 30, 2018 Property State
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Description Of Business [Line Items] |
Number of properties in portfolio | 932
Number of states in which our properties are located | State | 30
Third Parties [Member] |
Description Of Business [Line Items] |
Number of properties leased | 78
Owned Properties [Member] |
Description Of Business [Line Items] |
Number of properties | 854

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- Definition Description of business. + References No definition available. + Details
Name: | gty_DescriptionOfBusinessLineItems
Namespace Prefix: | gty_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of real estate properties in the portfolio, consisting of properties owned and properties leased from third party landlords. + References No definition available. + Details
Name: | gty_NumberOfPropertiesInPortfolio
Namespace Prefix: | gty_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of real estate properties leased from third-party landlords as of the balance sheet date. + References No definition available. + Details
Name: | gty_NumberOfPropertiesLeasedFromLandlords
Namespace Prefix: | gty_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of states in which the company's properties, comprised of those that are owned and those that are leased from third party landlords, are located. + References No definition available. + Details
Name: | gty_NumberOfStatesInWhichPropertiesAreLocated
Namespace Prefix: | gty_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfRealEstateProperties
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | us-gaap_CounterpartyNameAxis=gty_ThirdPartiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RealEstatePropertiesAxis=us-gaap_WhollyOwnedPropertiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |