Line of credit facility optional extended maturity date.

No definition available.

Name:	gty_LineOfCreditFacilityOptionalExtendedMaturityDate
Namespace Prefix:	gty_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The length of time the Revolving Facility may be extended.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateOriginalLoanAmountAxis=gty_SixthAmendedAndRestatedPrudentialAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=gty_SeriesQNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=gty_SeriesBNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Summary of Scheduled Debt Maturities, Including Balloon Payments (Parenthetical) (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Oct. 27, 2021
Revolving Facility [Member]
Debt Instrument [Line Items]
Senior unsecured note, aggregate amount issued			$ 300,000,000
Senior unsecured note purchase agreement, maturity date	Oct. 27, 2025	Oct. 27, 2025
Credit facility agreement, maturity date	Oct. 27, 2025
Revolving facility optional extension period	6 months
Credit facility agreement, optional extended maturity date	Oct. 31, 2026
Sixth Amended and Restated Prudential Agreement [Member] \| Series Q Notes [Member]
Debt Instrument [Line Items]
Senior unsecured note, aggregate amount issued	$ 80,000,000
Interest rate on agreement	3.65%
Senior unsecured note purchase agreement, maturity date	Jan. 20, 2033
Sixth Amended and Restated Prudential Agreement [Member] \| Series B Notes [Member]
Debt Instrument [Line Items]
Senior unsecured note, aggregate amount issued	$ 75,000,000
Interest rate on agreement	5.35%
Senior unsecured note purchase agreement, maturity date	Jun. 02, 2023