Organization - Additional Information (Detail) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2015 USD ($) Facility shares	Jun. 30, 2015 USD ($) States Property shares	Dec. 31, 2014 shares	Dec. 31, 2012 Property	Dec. 31, 2011 Property	Dec. 31, 2008 Property
Organization [Line Items]
Number of self-storage properties owned and managed		531
Number of states in which self-storage properties owned and managed | States		25
Number of properties managed with no ownership		20
Percentage of ownership interest of the subsidiary and its limited partnership which controls the operations of the Operating Partnership		99.50%
Units of redeemable noncontrolling interest in operating partnership | shares		178,866	155,484
Noncontrolling limited partnership unit redemption value		One common share or cash
Number of units issued for acquisition | shares	23,382
Fair value of units, issued for acquisition | $	$ 2.1	$ 2.1
Number of self storage properties acquired | Facility	1
Sovran HHF Storage Holdings LLC [Member]
Organization [Line Items]
Number of properties owned and managed under twenty-percent stake joint venture		39				25
Percentage ownership in unconsolidated joint venture		20.00%
Sovran HHF Storage Holdings II LLC [Member]
Organization [Line Items]
Percentage of variable interest ownership in unconsolidated joint venture		15.00%
Number of properties owned and managed under fifteen-percent stake joint venture		30		10	20
Geographic Concentration Risk [Member] | Texas and Florida [Member] | Revenue [Member]
Organization [Line Items]
Concentration risk, percentage		41.00%
Geographic Concentration Risk [Member] | Houston Texas [Member] | Revenue [Member]
Organization [Line Items]
Concentration risk, percentage		11.00%