Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Public Offerings (Details)

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Stockholders' Equity Public Offerings (Details) (USD $)
0 Months Ended 3 Months Ended
Feb. 24, 2012
Jan. 17, 2012
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2011
Class of Stock [Line Items]          
Payments of Stock Issuance Costs     $ 8,200,000    
Common Stock, Shares, Issued 30,000,000 34,000,000 214,207,346   140,596,708
Common Stock, Shares, Issued Pursuant to the Underwriters' Over-allotments 4,500,000 5,100,000      
Proceeds from Issuance of Common Stock 341,600,000 358,500,000 692,000,000 287,766,000  
Proceeds from Issuance of Common Stock, Net     $ 691,900,000    
Equity Issuance, Amount Per Share $ 9.90 $ 9.17