Credit and loan agreement.

No definition available.

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

- Definition

Debt instrument additional principal amount.

+ References

No definition available.

+ Details

Name:	gty_DebtInstrumentAdditionalPrincipalAmount
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument Initial Principal Amount

+ References

No definition available.

+ Details

Name:	gty_DebtInstrumentInitialPrincipalAmount
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The increase in basis points to the base interest rate in the event of a default on the credit agreement.

+ References

No definition available.

+ Details

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

- Definition

Line of credit facility, extension term.

+ References

No definition available.

+ Details

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

- Definition

Line of credit facility maturity date.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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

- Definition

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

+ References

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

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-Topic 815
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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Debt - Additional Information (Detail) - USD ($)	1 Months Ended				9 Months Ended
Debt - Additional Information (Detail) - USD ($)	Oct. 31, 2023	Jan. 31, 2023	Feb. 28, 2022	Oct. 31, 2021	Sep. 30, 2024	Jun. 21, 2018
Credit and Loan Agreement [Line Items]
Notional Amount	$ 75,000,000
Fifth Amended and Restated Prudential Agreement [Member]
Credit and Loan Agreement [Line Items]
Amount of rate increase in case of default					2.00%
Second Amended and Restated AIG Agreement [Member] \| Series L Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 55,000,000
Interest Rate			3.45%
Maturity Date			Feb. 22, 2032
First Amended and Restated AIG Agreement [Member] \| Series G Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			3.52%
Maturity Date			Sep. 12, 2029
First Amended and Restated AIG Agreement [Member] \| Series J Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			3.43%
Maturity Date			Nov. 25, 2030
First Amended and Restated MassMutual Agreement [Member] \| Series H Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 25,000,000
Interest Rate			3.52%
Maturity Date			Sep. 12, 2029
First Amended and Restated MassMutual Agreement [Member] \| Series K Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 25,000,000
Interest Rate			3.43%
Maturity Date			Nov. 25, 2030
First Amended and Restated MassMutual Agreement [Member] \| Series M Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 20,000,000
Interest Rate			3.45%
Maturity Date			Feb. 22, 2032
First Amended and Restated MassMutual Agreement [Member] \| Series O Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount		$ 20,000,000
Interest Rate		3.65%
Maturity Date		Jan. 20, 2033
Sixth Amended And Restated Prudential Agreement [Member] \| Series B Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 75,000,000
Interest Rate			5.35%
Maturity Date			Jun. 02, 2023
Sixth Amended And Restated Prudential Agreement [Member] \| Series C Guaranteed Senior Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			4.75%
Maturity Date			Feb. 25, 2025
Sixth Amended And Restated Prudential Agreement [Member] \| Series D Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			5.47%
Maturity Date			Jun. 21, 2028
Sixth Amended And Restated Prudential Agreement [Member] \| Series F Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			3.52%
Maturity Date			Sep. 12, 2029
Sixth Amended And Restated Prudential Agreement [Member] \| Series I Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 100,000,000
Interest Rate			3.43%
Maturity Date			Nov. 25, 2030
Sixth Amended And Restated Prudential Agreement [Member] \| Series Q Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 80,000,000
Interest Rate			3.65%
Maturity Date			Jan. 20, 2033
New York Life Agreement [Member] \| Series N Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 25,000,000
Interest Rate			3.45%
Maturity Date			Feb. 22, 2032
New York Life Agreement [Member] \| Series P Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount		$ 25,000,000
Interest Rate		3.65%
Maturity Date		Jan. 20, 2033
Met Life Agreement [Member] \| Series E Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount						$ 50,000,000
Interest Rate						5.47%
Maturity Date			Jun. 21, 2028
Revolving Credit Facility [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount				$ 300,000,000
Line of credit facility, maturity date				Oct. 27, 2025
Line of credit facility, extension term					two six-month extensions (for a total of 12 months)
Interest Rate					6.70%
Maturity Date					Oct. 27, 2025
Revolving Credit Facility [Member] \| SOFR [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate					0.10%
Revolving Credit Facility [Member] \| Maximum [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount				$ 300,000,000
Annual commitment fee on undrawn funds					0.25%
Revolving Credit Facility [Member] \| Maximum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate					1.90%
Revolving Credit Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate					0.90%
Revolving Credit Facility [Member] \| Minimum [Member]
Credit and Loan Agreement [Line Items]
Annual commitment fee on undrawn funds					0.15%
Revolving Credit Facility [Member] \| Minimum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate					1.30%
Revolving Credit Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate					0.30%
Term Loan [Member]
Credit and Loan Agreement [Line Items]
Interest Rate					6.13%
Maturity Date					Oct. 17, 2025
Term Loan [Member] \| Line of Credit [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount	150,000,000
Debt instrument initial principal amount	$ 75,000,000
Line of credit facility, maturity date	Oct. 17, 2025
Line of credit facility, extension term	one twelve-month
Debt instrument additional principal amount	$ 75,000,000
Term Loan [Member] \| Line of Credit [Member] \| SOFR [Member]
Credit and Loan Agreement [Line Items]
Weighted average interest rate	4.73%
Effective fixed interest rate					6.13%
Notional Amount	$ 150,000,000
Term Loan [Member] \| Line of Credit [Member] \| SOFR Adjustment [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate	0.10%
Term Loan [Member] \| Line of Credit [Member] \| Maximum [Member] \| SOFR Adjustment [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate	1.90%
Term Loan [Member] \| Line of Credit [Member] \| Maximum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate	0.90%
Term Loan [Member] \| Line of Credit [Member] \| Minimum [Member] \| SOFR Adjustment [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate	1.30%
Term Loan [Member] \| Line of Credit [Member] \| Minimum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate	0.30%