Investment In Storage Facilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Finite-Lived Intangible Assets [Line Items]
Amortization period for in-place customer leases on a straight-line basis			12 months
Amortization expense related to in-place customer leases	$ 1.0	$ 0.3	$ 2.8	$ 0.6
Subsequent [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 3.3		$ 3.3