Credit and loan agreement.

No definition available.

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

- 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

Unamortized debt issuance costs.

+ References

No definition available.

+ Details

Name:	gty_UnamortizedDebtIssuanceCosts
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

+ 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

+ Details

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

- 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

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

Debt - Additional Information (Detail) - USD ($)	1 Months Ended					6 Months Ended
Debt - Additional Information (Detail) - USD ($)	Nov. 30, 2025	Jan. 31, 2025	Nov. 30, 2024	Oct. 31, 2023	Feb. 28, 2022	Jun. 30, 2026	Jun. 30, 2018
Credit and Loan Agreement [Line Items]
Unamortized debt issuance costs						$ 900,000
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
Second Amended and Restated AIG Agreement [Member] \| Series M Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount					$ 20,000,000
Interest Rate					3.45%
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						3.43%
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
Maturity Date						Nov. 25, 2030
First Amended and Restated MassMutual Agreement [Member] \| Series M Notes [Member]
Credit and Loan Agreement [Line Items]
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
Seventh Amended And Restated Prudential Agreement [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Seventh Amended And Restated Prudential Agreement [Member] \| Series C Notes [Member]
Credit and Loan Agreement [Line Items]
Interest Rate			4.75%
Maturity Date			Feb. 25, 2025
Seventh 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
Seventh 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
Seventh 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
Seventh Amended And Restated Prudential Agreement [Member] \| Series T Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			5.70%
Maturity Date			Feb. 22, 2032
Seventh 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
New York Life Agreement [Member] \| Series R Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 50,000,000
Interest Rate			5.52%
Maturity Date			Sep. 12, 2029
New York Life Agreement [Member] \| Series S Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount			$ 25,000,000
Interest Rate			5.70%
Maturity Date			Feb. 22, 2032
Multiple Purchasers Party Agreement [Member] \| Series U Notes [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount	$ 250,000,000
Interest Rate	5.76%
Maturity Date	Jan. 22, 2036
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
Credit Facility [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount		$ 450,000,000
Line of credit facility, maturity date		Jan. 31, 2029
Line of credit facility, extension term						two six-month extensions (for a total of 12 months)
Interest Rate						5.01%
Maturity Date						Jan. 31, 2029
Credit Facility [Member] \| SOFR [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate						0.10%
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%
Credit Facility [Member] \| Maximum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate						1.90%
Credit Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate						0.90%
Credit Facility [Member] \| Minimum [Member]
Credit and Loan Agreement [Line Items]
Annual commitment fee on undrawn funds						0.15%
Credit Facility [Member] \| Minimum [Member] \| Base Rate [Member]
Credit and Loan Agreement [Line Items]
Credit agreement margin on borrowing base rate						1.30%
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] \| Line of Credit [Member]
Credit and Loan Agreement [Line Items]
Aggregate principal amount				$ 150,000,000
Line of credit facility, maturity date				Oct. 17, 2025
Line of credit facility, extension term				one twelve-month