Investment in Joint Ventures - Summary of Unconsolidated Joint Ventures' Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Investment in storage facilities, net	$ 1,958,972		$ 1,958,972		$ 1,766,282
Other assets	9,067		9,067		9,298
Total Assets	2,044,952		2,044,952		1,854,800
Mortgages payable	2,061		2,061		2,127
Total Liabilities	907,887		907,887		865,309
Company equity (deficiency)	1,121,323		1,121,323		975,869
Depreciation and amortization of customer list	(14,584)	$ (12,481)	(28,766)	$ (24,423)	(51,749)	$ (45,233)	$ (40,542)
Income tax expense	(600)	(300)	(1,000)	(600)
Interest expense	(9,216)	$ (8,872)	(18,377)	$ (16,216)	$ (34,578)	$ (32,000)	$ (33,166)
Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investment in storage facilities, net	338,682		338,682
Other assets	7,175		7,175
Total Assets	345,857		345,857
Due to the Company	426		426
Mortgages payable	124,149		124,149
Other liabilities	4,416		4,416
Total Liabilities	128,991		128,991
Unaffiliated partners' equity (deficiency)	173,493		173,493
Company equity (deficiency)	43,373		43,373
Total Partners' Equity (Deficiency)	216,866		216,866
Total Liabilities and Partners' Equity (Deficiency)	345,857		345,857
Total revenues			19,374
Property operating expenses			(6,398)
Administrative, management and call center fees			(1,437)
Depreciation and amortization of customer list			(4,320)
Income tax expense			(88)
Interest expense			(2,927)
Net income			4,204
Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investment in storage facilities, net	183,575		183,575
Other assets	4,862		4,862
Total Assets	188,437		188,437
Due to the Company	391		391
Mortgages payable	102,509		102,509
Other liabilities	2,360		2,360
Total Liabilities	105,260		105,260
Unaffiliated partners' equity (deficiency)	70,707		70,707
Company equity (deficiency)	12,470		12,470
Total Partners' Equity (Deficiency)	83,177		83,177
Total Liabilities and Partners' Equity (Deficiency)	188,437		188,437
Total revenues			14,657
Property operating expenses			(5,107)
Administrative, management and call center fees			(1,086)
Depreciation and amortization of customer list			(2,099)
Income tax expense			(18)
Interest expense			(2,652)
Net income			3,695
Iskalo Office Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investment in office building	4,919		4,919
Other assets	3,238		3,238
Total Assets	8,157		8,157
Mortgages payable	9,137		9,137
Other liabilities	333		333
Total Liabilities	9,470		9,470
Unaffiliated partners' equity (deficiency)	(745)		(745)
Company equity (deficiency)	(568)		(568)
Total Partners' Equity (Deficiency)	(1,313)		(1,313)
Total Liabilities and Partners' Equity (Deficiency)	$ 8,157		8,157
Total revenues			763
Property operating expenses			(293)
Depreciation and amortization of customer list			(114)
Interest expense			(144)
Net income			$ 212