Property Acquisitions - Additional Information (Detail)					12 Months Ended
	Nov. 22, 2019 USD ($) Property Option	Jun. 17, 2019 USD ($) Property Option	Aug. 01, 2018 USD ($) Property Option	Apr. 17, 2018 USD ($) Property Option	Dec. 31, 2019 USD ($) Property	Dec. 31, 2018 USD ($) Property
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property					27	41
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period					$ 87,157,000	$ 77,972,000
1234M Division Street Inc [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property		6
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period		$ 24,724,000
Unitary lease description					The unitary lease requires 1234 M to pay a fixed annual rent plus all amounts pertaining to the properties, including environmental expenses, real estate taxes, assessments, license and permit fees, charges for public utilities and all other governmental charges. Rent is scheduled to increase annually during the initial and renewal terms of the lease.
Unitary lease initial term		15 years
Number of unitary lease renewal options | Option		2
Unitary lease renewal term		10 years
Purchase price allocation, land acquired		$ 18,086,000
Purchase price allocation, buildings and improvements acquired		4,789,000
Purchase price allocated to in-place leases		$ 1,849,000
QNC OpCo Inc [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property	4
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period	$ 14,144,000
Unitary lease description					The unitary lease requires QNC to pay a fixed annual rent plus all amounts pertaining to the properties, including environmental expenses, real estate taxes, assessments, license and permit fees, charges for public utilities and all other governmental charges. Rent is scheduled to increase annually during the initial and renewal terms of the lease.
Unitary lease initial term	15 years
Number of unitary lease renewal options | Option	5
Unitary lease renewal term	5 years
Purchase price allocation, land acquired	$ 2,663,000
Purchase price allocation, buildings and improvements acquired	10,469,000
Purchase price allocated to in-place leases	$ 1,012,000
Gasoline Stations and Convenience Store Properties [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property					17
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period					$ 48,290,000
Other Acquisition [Member]
Business Acquisition [Line Items]
Purchase price allocation, land acquired					18,820,000
Purchase price allocation, buildings and improvements acquired					26,790,000
Purchase price allocated to in-place leases					2,744,000
Purchase price allocated to above market leases					277,000
Purchase price allocated to below market leases					$ 341,000
GPM Investments, LLC [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property				30		5
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period				$ 52,592,000		$ 7,968,000
Unitary lease description					The unitary lease requires GPM to pay a fixed annual rent plus all amounts pertaining to the properties, including environmental expenses, real estate taxes, assessments, license and permit fees, charges for public utilities and all other governmental charges. Rent is scheduled to increase annually during the initial and renewal terms of the lease.
Unitary lease initial term				15 years
Number of unitary lease renewal options | Option				4
Unitary lease renewal term				5 years
Purchase price allocation, land acquired				$ 31,633,000		4,929,000
Purchase price allocation, buildings and improvements acquired				17,489,000		2,753,000
Purchase price allocated to in-place leases				4,047,000		$ 286,000
Purchase price allocated to below market leases				$ 577,000
Applegreen PLC [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property			6
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period			$ 17,412,000
Unitary lease description					The unitary lease requires Applegreen to pay a fixed annual rent plus all amounts pertaining to the properties, including environmental expenses, real estate taxes, assessments, license and permit fees, charges for public utilities and all other governmental charges. Rent is scheduled to increase annually during the initial and renewal terms of the lease.
Unitary lease initial term			15 years
Number of unitary lease renewal options | Option			4
Unitary lease renewal term			5 years
Purchase price allocation, land acquired			$ 8,930,000
Purchase price allocation, buildings and improvements acquired			6,773,000
Purchase price allocated to in-place leases			1,371,000
Purchase price allocated to above market leases			773,000
Purchase price allocated to below market leases			$ 435,000