Property Acquisitions - Additional Information (Detail)				6 Months Ended
	Apr. 17, 2018 USD ($) Property Option	Oct. 03, 2017 USD ($) Property Option Restaurant	Sep. 06, 2017 USD ($) Property Option	Jun. 30, 2018 USD ($) Property	Jun. 30, 2017 USD ($) Property
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property					10
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period				$ 55,308,000	$ 17,800,000
Number of stand-alone Burger King quick service restaurants acquired during the period | Restaurant		5
GPM Investments, LLC [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property	30			2
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period	$ 52,592,000			$ 2,716,000
Unitary lease description				The unitary lease provides for an initial term of 15 years, with four five-year renewal options. The unitary lease requires GPM to pay a fixed annual rent plus all amounts pertaining to the GPM 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
Purchase price allocation, buildings and improvements acquired	17,489,000
Purchase price allocated to in-place leases	4,047,000
Purchase price allocated to below market leases	$ 577,000
GPM Investments, LLC [Member] | Land [Member]
Business Acquisition [Line Items]
Purchase price allocation, land acquired				$ 1,207,000
GPM Investments, LLC [Member] | Building and Building Improvements [Member]
Business Acquisition [Line Items]
Purchase price allocation, buildings and improvements acquired				1,326,000
GPM Investments, LLC [Member] | In-Place Leases [Member]
Business Acquisition [Line Items]
Purchase price allocated to in-place leases				$ 183,000
Gasoline Stations and Convenience Store Properties [Member]
Business Acquisition [Line Items]
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period					17,800,000
Gasoline Stations and Convenience Store Properties [Member] | Land [Member]
Business Acquisition [Line Items]
Purchase price allocation, land acquired					3,825,000
Gasoline Stations and Convenience Store Properties [Member] | Building and Building Improvements [Member]
Business Acquisition [Line Items]
Purchase price allocation, buildings and improvements acquired					12,000,000
Gasoline Stations and Convenience Store Properties [Member] | In-Place Leases [Member]
Business Acquisition [Line Items]
Purchase price allocated to in-place leases					$ 1,975,000
Empire Petroleum Partners, LLC [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property			49
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period			$ 123,126,000
Unitary lease description				The unitary lease provides for an initial term of 15 years, with four five-year renewal options. The unitary lease requires Empire to pay a fixed annual rent plus all amounts pertaining to the Empire 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			$ 75,674,000
Purchase price allocation, buildings and improvements acquired			38,205,000
Purchase price allocated to in-place leases			9,058,000
Purchase price allocated to above market leases			$ 189,000
Applegreen PLC [Member]
Business Acquisition [Line Items]
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period		$ 68,710,000
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		$ 36,874,000
Purchase price allocation, buildings and improvements acquired		27,431,000
Purchase price allocated to in-place leases		4,548,000
Purchase price allocated to below market leases		1,104,000
Purchase price allocated to above market leases		$ 961,000
Number of convenience stores and gasoline stations | Property		33