Investment in Real Estate - Additional Information (Detail) (USD $) In Billions, unless otherwise specified	12 Months Ended		9 Months Ended
Dec. 31, 2011	May 31, 2011	Sep. 30, 2012 Purchase Price Allocation Adjustments
Real Estate Properties [Line Items]
Asset acquisition price adjustments period			1 year
Number of closed acquisition properties	75
Number of acquired sites	30,129
Purchase price to acquire properties	$ 1.50	$ 1.43

The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant