Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Parenthetical) (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) Property	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Property Facility Store
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property	0
Mortgages payable	$ 12,581		$ 12,674
Distributions from unconsolidated joint ventures	2,037	$ 1,357
Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from unconsolidated joint ventures	1,400
Excess of investment over net asset due to capitalization of acquisition related costs	1,700
Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from unconsolidated joint ventures	500
191 III Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from unconsolidated joint ventures	100
Iskalo Office Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from unconsolidated joint ventures	100
Rent paid during the period	300	$ 300
Urban Box Coralway Storage, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital	300
SNL/Orix 1200 McDonald Ave., LLC [Member]
Schedule of Equity Method Investments [Line Items]
Non-recourse mortgage loan principal outstanding	6,700
SNL Orix Merrick, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Non-recourse mortgage loan principal outstanding	10,400
Review Avenue Partners LLC [Member] | Common Stock Shares [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital	$ 100
Arizona [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	11
Colorado [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	4
Florida [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	3
Georgia [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	1
Georgia [Member] | Life Storage-SERS Storage LLC [Member] | Additional Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property	3		3
Payment for property acquisition			$ 39,100
Mortgages payable			$ 22,000
Kentucky [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	2
Nevada [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	5
New Jersey [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	2
New Jersey [Member] | Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	17
Ohio [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	6
Pennsylvania [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	1
Pennsylvania [Member] | Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	3
Tennessee [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	2
Texas [Member] | Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	20
Texas [Member] | Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	10
Arizona, Nevada and Tennessee [Member] | Sovran HHF Storage Holdings LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Facility			18
Payment for property acquisition			$ 330,000
Mortgages payable			$ 135,000
Number of properties collateral for debt | Store			16
Contribution of company to joint venture as share in capital	$ 200
California [Member] | 191 III Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of self-storage facilities | Property	6
California [Member] | 191 III Holdings LLC [Member] | Six Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property	6
Payment for property acquisition	$ 104,100
Mortgages payable	57,200
Contribution of company to joint venture as share in capital	$ 100