Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity of the Company Common Share Offering (Details)

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Shareholders' Equity of the Company Common Share Offering (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Units
Entity Information [Line Items]  
Stock Issued During Period, Shares, New Issues 4.6
Stock Issued During Period Per Share Amount $ 25.662
Number of Common General Partnership Units Received in Exchange for Contributed Net Proceeds of Share Offering 13,000
Number of Common Limited Partnership Units Received in Exchange for Contributed Net Proceeds of Share Offering 1,137,000