Investment in Storage Facilities and Intangible Assets - Schedule of Purchase Price of Facilities Acquired (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) Property	Mar. 31, 2020 Property
Investment Holdings [Line Items]
Number of Properties | Property	16	6
Purchase Price	$ 266,215
Consideration paid, Cash Paid	265,197
Consideration paid, Net Other Liabilities (Assets) Assumed	1,018
Acquisition Date Fair Value, In-Place Customer Leases	2,888
Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	39,401
Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 223,898
SC [Member] | Asset Acquired on 1/4/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Jan. 04, 2021
Purchase Price	$ 8,070
Consideration paid, Cash Paid	8,042
Consideration paid, Net Other Liabilities (Assets) Assumed	28
Acquisition Date Fair Value, In-Place Customer Leases	105
SC [Member] | Asset Acquired on 1/4/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	812
SC [Member] | Asset Acquired on 1/4/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 7,153
CA [Member] | Asset Acquired on 1/21/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Jan. 21, 2021
Purchase Price	$ 18,287
Consideration paid, Cash Paid	18,251
Consideration paid, Net Other Liabilities (Assets) Assumed	36
Acquisition Date Fair Value, In-Place Customer Leases	135
CA [Member] | Asset Acquired on 1/21/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	1,322
CA [Member] | Asset Acquired on 1/21/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 16,830
NY [Member] | Asset Acquired on 3/4/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	1
Date of Acquisition	Mar. 04, 2021
Purchase Price	$ 47,947
Consideration paid, Cash Paid	47,933
Consideration paid, Net Other Liabilities (Assets) Assumed	14
Acquisition Date Fair Value, In-Place Customer Leases	336
NY [Member] | Asset Acquired on 3/4/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	10,591
NY [Member] | Asset Acquired on 3/4/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 37,020
Florida [Member] | Asset Acquired on 3/11/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	8
Date of Acquisition	Mar. 11, 2021
Purchase Price	$ 85,156
Consideration paid, Cash Paid	84,586
Consideration paid, Net Other Liabilities (Assets) Assumed	570
Acquisition Date Fair Value, In-Place Customer Leases	1,237
Florida [Member] | Asset Acquired on 3/11/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	13,381
Florida [Member] | Asset Acquired on 3/11/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 70,538
AZ [Member] | Asset Acquired on 3/24/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	3
Date of Acquisition	Mar. 24, 2021
Purchase Price	$ 67,089
Consideration paid, Cash Paid	66,890
Consideration paid, Net Other Liabilities (Assets) Assumed	199
Acquisition Date Fair Value, In-Place Customer Leases	632
AZ [Member] | Asset Acquired on 3/24/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	7,129
AZ [Member] | Asset Acquired on 3/24/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 59,320
WA [Member] | Asset Acquired on 3/25/2021 [Member]
Investment Holdings [Line Items]
Number of Properties | Property	2
Date of Acquisition	Mar. 25, 2021
Purchase Price	$ 39,666
Consideration paid, Cash Paid	39,495
Consideration paid, Net Other Liabilities (Assets) Assumed	171
Acquisition Date Fair Value, In-Place Customer Leases	443
WA [Member] | Asset Acquired on 3/25/2021 [Member] | Land [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	6,166
WA [Member] | Asset Acquired on 3/25/2021 [Member] | Building, Equipment and Improvements [Member]
Investment Holdings [Line Items]
Acquisition Date Fair Value, Fixed Assets	$ 33,037