Investment in Storage Facilities and Intangible Assets - Schedule of Purchase Price of Facilities Acquired (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) Property
Investment Holdings [Line Items]
Number of Properties | Property	6
Purchase Price	$ 109,682
Consideration paid, Cash Paid	98,526
Consideration paid, Carrying Value of Noncontrolling Interest in Joint Venture	10,715
Consideration paid, Net Other Liabilities (Assets) Assumed	441
Acquisition Date Fair Value, In-Place Customer Leases	1,326
Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	36,257
Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 72,099
NY [Member] | Asset Acquired on 1/16/2019 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Jan. 16, 2019
Purchase Price	$ 57,169
Consideration paid, Cash Paid	46,402
Consideration paid, Carrying Value of Noncontrolling Interest in Joint Venture	10,715
Consideration paid, Net Other Liabilities (Assets) Assumed	52
Acquisition Date Fair Value, In-Place Customer Leases	277
NY [Member] | Asset Acquired on 1/16/2019 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	30,029
NY [Member] | Asset Acquired on 1/16/2019 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 26,863
Florida [Member] | Asset Acquired on 3/8/2019 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Mar. 08, 2019
Purchase Price	$ 9,302
Consideration paid, Cash Paid	9,222
Consideration paid, Net Other Liabilities (Assets) Assumed	80
Acquisition Date Fair Value, In-Place Customer Leases	108
Florida [Member] | Asset Acquired on 3/8/2019 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	1,817
Florida [Member] | Asset Acquired on 3/8/2019 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 7,377
Florida [Member] | Asset Acquired on 6/11/2019 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Jun. 11, 2019
Purchase Price	$ 9,955
Consideration paid, Cash Paid	9,926
Consideration paid, Net Other Liabilities (Assets) Assumed	29
Acquisition Date Fair Value, In-Place Customer Leases	85
Florida [Member] | Asset Acquired on 6/11/2019 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	662
Florida [Member] | Asset Acquired on 6/11/2019 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 9,208
OH [Member] | Asset Acquired on 4/30/2019 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	3
Date of Acquisition	Apr. 30, 2019
Purchase Price	$ 33,256
Consideration paid, Cash Paid	32,976
Consideration paid, Net Other Liabilities (Assets) Assumed	280
Acquisition Date Fair Value, In-Place Customer Leases	856
OH [Member] | Asset Acquired on 4/30/2019 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	3,749
OH [Member] | Asset Acquired on 4/30/2019 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 28,651