Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity Public Offerings (Details)

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Stockholders' Equity Public Offerings (Details) (USD $)
3 Months Ended 12 Months Ended
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Jul. 15, 2011
May 25, 2011
Mar. 16, 2011
Class of Stock [Line Items]                  
Payments of Stock Issuance Costs       $ 17,600,000          
Common Stock, Shares, Issued       140,596,708 40,501,212   42,000,000 20,000,000 25,000,000
Common Stock, Shares, Issued Pursuant to the Underwriters' Over-allotments             6,300,000 3,000,000 3,750,000
Sale of Stock, Price Per Share             $ 10.15 $ 10.40 $ 10.25
Proceeds from Issuance of Common Stock 490,200,000 239,200,000 294,700,000 1,006,847,000 235,275,000 1,000      
Proceeds from Issuance of Common Stock, Net       $ 1,000,000,000