Value of input used to measure long lived assets.

No definition available.

Name:	gty_LongLivedAssetsMeasurementInput
Namespace Prefix:	gty_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Notes and mortgages receivable.

+ References

No definition available.

+ Details

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

- Definition

Organization consolidation and presentation of financial statements.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of annual assumed average rent increases used as an unobservable input to measure the fair value.

+ References

No definition available.

+ Details

Name:	gty_PercentageAnnualAssumedAverageRentIncreasesUnobservableInputs
Namespace Prefix:	gty_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Property plant and equipment assumed holding periods.

+ References

No definition available.

+ Details

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

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123351718&loc=d3e2420-110228

+ Details

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (c)

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

+ Details

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

- Definition

The cash inflow from borrowings to finance the cost of construction.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromConstructionLoansPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputExpectedTermMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputCapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_PropertyPlantAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis=gty_EstimatedSalePriceMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis=gty_DiscountedCashFlowMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis=gty_AccumulationOfAssetRetirementCostMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=gty_NotesAndMortgagesReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	$ 1,038,000	$ 776,000
Notes and mortgages receivable	$ 15,873,000		$ 14,699,000
Level 3 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Assumed annual average rent increases for unobservable inputs	2.00%
Level 3 [Member] \| Measurement Input Expected Term [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Assumed holding periods for unobservable inputs	15 years
Level 3 [Member] \| Measurement Input Cap Rate [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Real estate fair value, measurement input	8.00%
Level 3 [Member] \| Measurement Input Discount Rate [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Real estate fair value, measurement input	7.00%
Properties [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	$ 62,000	335,000
Estimated Sale Price Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	694,000
Discounted Cash Flow Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	0
Accumulation of Asset Retirement Cost Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	344,000
Construction Loans [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Notes and mortgages receivable	7,487,000
Notes and Mortgages Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	0	0
Direct Financing Leases Financing Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairments	0	$ 0
Accounting Standards Update 2016-13
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Additional allowance for credit losses			826,000
Proceeds from construction loans	1,782,000
Accounting Standards Update 2016-13 \| Notes and Mortgages Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Additional allowance for credit losses	0		$ 297,000
Accounting Standards Update 2016-13 \| Direct Financing Leases Financing Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Additional allowance for credit losses	$ 0