Investment in Storage Facilities and Intangible Assets - Schedule of Purchase Price of Facilities Acquired (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) Property
Investment Holdings [Line Items]
Number of Properties | Property	31
Purchase Price	$ 419,608
Consideration paid, Cash Paid	417,930
Consideration paid, Net Other Liabilities (Assets) Assumed	1,678
Acquisition Date Fair Value, In-Place Customer Leases	6,586
Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	52,862
Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	359,578
Construction in Progress [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 582
CA [Member] | Asset Acquired on 3/9/2020 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	6
Date of Acquisition	Mar. 09, 2020
Purchase Price	$ 124,298
Consideration paid, Cash Paid	124,204
Consideration paid, Net Other Liabilities (Assets) Assumed	94
Acquisition Date Fair Value, In-Place Customer Leases	1,675
CA [Member] | Asset Acquired on 3/9/2020 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	20,307
CA [Member] | Asset Acquired on 3/9/2020 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	101,734
CA [Member] | Asset Acquired on 3/9/2020 [Member] | Construction in Progress [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 582
FL, GA, NJ, OH, PA, TX [Member]
Investment Holdings [Line Items]
Number of Properties | Property	25
Date of Acquisition	Sep. 29, 2020
Purchase Price	$ 295,310
Consideration paid, Cash Paid	293,726
Consideration paid, Net Other Liabilities (Assets) Assumed	1,584
Acquisition Date Fair Value, In-Place Customer Leases	4,911
FL, GA, NJ, OH, PA, TX [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	32,555
FL, GA, NJ, OH, PA, TX [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 257,844