Investment In Joint Ventures - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Sovran HHF Storage Holdings II LLC [Member] Property	Sep. 30, 2011 Sovran HHF Storage Holdings II LLC [Member]	Dec. 31, 2011 Sovran HHF Storage Holdings II LLC [Member] Property	Sep. 30, 2012 Sovran HHF Storage Holdings LLC [Member]	Dec. 31, 2011 Sovran HHF Storage Holdings LLC [Member]	Dec. 31, 2008 Sovran HHF Storage Holdings LLC [Member] Property	Sep. 30, 2012 Sovran HHF And Sovran HHF II [Member]	Sep. 30, 2011 Sovran HHF And Sovran HHF II [Member]	Sep. 30, 2012 Sovran HHF And Sovran HHF II [Member]	Sep. 30, 2011 Sovran HHF And Sovran HHF II [Member]	Sep. 30, 2012 Iskalo Office Holdings, LLC [Member]	Sep. 30, 2011 Iskalo Office Holdings, LLC [Member]	Sep. 30, 2012 Iskalo Office Holdings, LLC [Member]	Sep. 30, 2011 Iskalo Office Holdings, LLC [Member]	Dec. 31, 2011 Iskalo Office Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest						15.00%			20.00%							49.00%		49.00%
Investment at carrying value	$ 34,524,000		$ 34,524,000		$ 31,939,000	$ 13,300,000			$ 21,200,000							$ (500,000)		$ (500,000)		$ (500,000)
Number of properties owned and managed under twenty-percent stake joint venture											25
Payment for properties acquisition	106,185,000		106,185,000			29,000,000		166,100,000			171,500,000
Contribution of company to joint venture as share in capital						2,300,000		12,800,000	1,200,000	800,000	18,600,000							196,049
Excess of investment over net asset due to capitalization of acquisition related costs									1,700,000
Number of properties owned and managed under fifteen-percent stake joint venture								20
Additional properties acquired						10
Management and call center fee as a percentage of revenue														7.00%
Management and call center fee earned												800,000	600,000	2,200,000	1,200,000
Acquisition fee received for securing purchases														200,000	700,000
Company's share in (loss) income of joint venture	335,000	(512,000)	608,000	(408,000)								340,000	(637,000)	574,000	(497,000)	(4,000)	(4,000)	9,000	(59,000)
Acquisition related costs						162,000	734,000
Property acquisition related costs included in other expenses						$ 1,100,000