Property Acquisitions - Additional Information (Detail)			12 Months Ended
	Oct. 03, 2017 USD ($) Property Option Restaurant	Sep. 06, 2017 USD ($) Property Option	Dec. 31, 2017 USD ($) Property	Dec. 31, 2016 USD ($) Property	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period			$ 214,000,000	$ 7,688,000	$ 219,192,000
Gasoline Stations and Convenience Store Properties [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property			103	3
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period			$ 214,000,000
Purchase price allocation, land acquired			5,800,000	$ 1,041,000
Purchase price allocation, buildings and improvements acquired			$ 14,424,000	6,111,000
Additional number of gasoline stations and convenience stores acquired during the period | Property			16
Additional aggregate purchase price of the gasoline stations and convenience stores acquired during the period			$ 22,164,000
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period				7,688,000
Transaction cost related to acquisition				86,000
Gasoline Stations and Convenience Store Properties [Member] | Land, Buildings and Improvements [Member]
Business Acquisition [Line Items]
Purchase price allocated to in-place leases			2,969,000	374,000
Purchase price allocated to below market leases			$ 1,028,000
Gasoline Stations and Convenience Store Properties [Member] | Parcel of Land [Member]
Business Acquisition [Line Items]
Purchase price allocation, land acquired				162,000
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 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
Empire Petroleum Partners, LLC [Member] | Land, Buildings and Improvements [Member]
Business Acquisition [Line Items]
Purchase price allocated to above market leases		189,000
Purchase price allocated to in-place leases		$ 9,058,000
Applegreen PLC [Member]
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property	38
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	$ 36,874,000,000
Purchase price allocation, buildings and improvements acquired	27,431,000,000
Purchase price allocated to above market leases	961,000,000
Purchase price allocated to in-place leases	$ 4,548,000,000
Number of convenience stores and gasoline stations | Property	33
Number of stand-alone Burger King quick service restaurants acquired during the period | Restaurant	5
Purchase price allocated to below market leases	$ 1,104,000,000
United Oil Transaction [Member]
Business Acquisition [Line Items]
Total revenues from continuing operations			$ 17,625,000	17,631,000	10,177,000
Net earnings from continuing operations			$ 12,087,000	$ 11,762,000	$ 6,952,000