Leases - Leasing Activities - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015 Property Portfolios	Mar. 31, 2014
Leases [Line Items]
Number of new triple net leases entered into during the period	15
Number of leased properties with new tenants	442
Properties under license agreements	21gty_PropertiesUnderLicenseAgreements
Maximum lease commitment for capital expenditure	$ 13,287,000
Co investment with tenants on capital expenditure, period	5 years
Asset retirement obligations removed from balance sheet	12,954,000
Deferred rental revenue	2,416,000us-gaap_DeferredRevenueLeasesGross
Lease origination costs	90,000us-gaap_DeferredCostsLeasingNet	0us-gaap_DeferredCostsLeasingNet
USTs [Member]
Leases [Line Items]
Asset retirement obligations removed from balance sheet	12,954,000
Net asset cost related to USTs removed from the balance sheet	10,538,000
Deferred rental revenue	$ 2,416,000
Minimum [Member]
Leases [Line Items]
Unitary triple-net lease agreements initial terms	15 years
Maximum [Member]
Leases [Line Items]
Unitary triple-net lease agreements successive terms	20 years

The number of years remaining in the Company's commitment to co-invest for a portion of capital expenditures.

No definition available.

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

- Details

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

- Definition

The maximum dollar amount the company has committed to co-invest with tenants for capital expenditures.

+ References

No definition available.

+ Details

Name:	gty_MaximumLeaseCommitmentForCapitalExpenditure
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of net asset retirement costs related to underground storage tanks removed from the balance sheet in conjunction with a transfer of related obligations to the lessee.

+ References

No definition available.

+ Details

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

- Definition

The number of leased properties with new tenants.

+ References

No definition available.

+ Details

Name:	gty_NumberOfLeasedPropertiesWithNewTenants
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of new triple-net leases entered into with petroleum distributors.

+ References

No definition available.

+ Details

Name:	gty_NumberOfNewTripleNetLeasesEnteredInto
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of years in the initial term under unitary triple-net lease agreements.

+ References

No definition available.

+ Details

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

- Definition

The number of years in the successive renewal term under unitary triple-net lease agreements.

+ References

No definition available.

+ Details

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

- Definition

Properties under license agreements, generally month to month.

+ References

No definition available.

+ Details

Name:	gty_PropertiesUnderLicenseAgreements
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

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

- Definition

This element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This element is net of accumulated amortization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40246-112709

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6453741&loc=d3e40879-112712

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40588-112709

+ Details

Name:	us-gaap_DeferredCostsLeasingNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents revenue received, but not recognized for financial reporting purposes. Such deferred revenue may consist of and include amounts paid in advance by lessees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 50

-Paragraph 4

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=25496975&loc=d3e45377-112738

+ Details

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

- Details

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- Details

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