Leases - Major Tenants - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016 Property Lease Tenants	Dec. 31, 2015
Leases [Line Items]
Number of significant tenants \| Tenants	3
Subsidiaries of Global Partners LP (NYSE GLP) [Member]
Leases [Line Items]
Number of leased properties \| Property	166
Number of unitary leases	2
Lease revenue percentage	21.00%	21.00%
Number of leased properties guaranteed	3
Subsidiaries of Chestnut Petroleum Dist. Inc.[Member]
Leases [Line Items]
Number of leased properties \| Property	79
Number of unitary leases	3
Lease revenue percentage	15.00%	16.00%
Number of leased properties guaranteed	57
Apro, LLC (d/b/a United Oil) [Member]
Leases [Line Items]
Number of leased properties \| Property	77
Number of unitary leases	3
Lease revenue percentage	15.00%	9.00%

The aggregate lease revenue from subsidiaries of our tenant as a percentage of our total revenue.

No definition available.

Name:	gty_LeaseRevenuePercentageOfRevenue
Namespace Prefix:	gty_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Leases.

No definition available.

The aggregate number of properties currently being leased to subsidiaries of our tenant.

No definition available.

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

Number of leased properties guaranteed.

No definition available.

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

The number of current tenants that are considered significant.

No definition available.

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

The number of unitary leases with subsidiaries of the tenant's parent.

No definition available.

The number of unitary leases that are guaranteed by the parent company.

No definition available.

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

Name:	us-gaap_LeaseArrangementTypeAxis=gty_SubsidiariesOfGlobalPartnersLpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LeaseArrangementTypeAxis=gty_SubsidiariesOfChestnutPetroleumDistIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LeaseArrangementTypeAxis=gty_AproLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: