Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Detail) $ in Thousands	Jun. 30, 2018 USD ($) Property	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Carrying value of investment	$ 133,225	$ 133,458
Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	57
Company common ownership interest	20.00%
Carrying value of investment	$ 84,000	85,100
Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	30
Company common ownership interest	15.00%
Carrying value of investment	$ 13,200	13,300
191 III Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	6
Company common ownership interest	20.00%
Carrying value of investment	$ 9,300	9,400
Life Storage-SERS Storage LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	3
Company common ownership interest	20.00%
Carrying value of investment	$ 3,600	3,600
Iskalo Office Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Company common ownership interest	49.00%
Carrying value of investment	$ (400)	(400)
Urban Box Coralway Storage, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	85.00%
Carrying value of investment	$ 4,400	4,100
SNL/Orix 1200 McDonald Ave., LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	5.00%
Carrying value of investment	$ 2,700	2,700
SNL Orix Merrick, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	5.00%
Carrying value of investment	$ 2,400	2,500
Review Avenue Partners LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	40.00%
Carrying value of investment	$ 11,300	11,500
N 32nd Street Self Storage, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	46.00%
Carrying value of investment	$ 1,300	$ 1,300
NYX Don Mills Storage LP [Member]
Schedule of Equity Method Investments [Line Items]
Number of Properties | Property	1
Company common ownership interest	17.00%
Carrying value of investment	$ 1,000