Property Acquisitions - Additional Information (Detail)					6 Months Ended		12 Months Ended
	Feb. 26, 2020 USD ($) Property Option	Feb. 04, 2020 USD ($) Property Option	Nov. 22, 2019 USD ($) Property Option	Jun. 17, 2019 USD ($) Property Option	Jun. 30, 2020 USD ($) Property	Jun. 30, 2019 USD ($) Property	Dec. 31, 2019 USD ($) Property
Business Acquisition [Line Items]
Number of gasoline stations and convenience stores acquired during the period | Property	10	10		6	15	9	27
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period	$ 50,303,000	$ 50,303,000		$ 24,724,000	$ 68,671,000	$ 29,700,000	$ 87,157,000
Unitary lease description					The unitary lease requires our tenant 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	15 years		15 years
Number of unitary lease renewal options | Option	5	5		2
Unitary lease renewal term	5 years	5 years		10 years
Purchase price allocation, land acquired	$ 4,775,000	$ 4,775,000		$ 18,086,000
Purchase price allocation, buildings and improvements acquired	41,093,000	41,093,000		4,789,000
Purchase price allocated to in-place leases	3,727,000	3,727,000		$ 1,849,000
Purchase price allocated to above market leases	1,955,000	1,955,000
Purchase price allocated to below market leases	$ 1,247,000	$ 1,247,000
Convenience Store, Gasoline Station And Other Automotive Related Properties [Member]
Business Acquisition [Line Items]
Aggregate purchase price of the gasoline stations and convenience stores acquired during the period					$ 18,368,000	$ 4,976,000
Number of convenience store, gasoline station and other automotive related acquired during the period | Property					5	3
Other Acquisition [Member]
Business Acquisition [Line Items]
Purchase price allocation, land acquired					$ 7,886,000	$ 3,075,000	18,820,000
Purchase price allocation, buildings and improvements acquired					9,508,000	1,813,000	26,790,000
Purchase price allocated to in-place leases					$ 974,000	$ 88,000	2,744,000
Purchase price allocated to above market leases							277,000
Purchase price allocated to below market leases							$ 341,000
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
Unitary lease description					The unitary lease provides for an initial term of 15 years, with two ten-year renewal options. The unitary lease requires our tenant 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.
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