Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity Public Offerings (Details)

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Stockholders' Equity Public Offerings (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
1 Months Ended 0 Months Ended 12 Months Ended
Jul. 18, 2012
Feb. 24, 2012
Jan. 17, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Class of Stock [Line Items]            
Common Stock, Shares, Issued 50,000,000 30,000,000 34,000,000 298,813,258 140,596,708  
Common Stock, Shares, Issued Pursuant to the Underwriters' Over-allotments 7,500,000 4,500,000 5,100,000      
Sale of Stock, Price Per Share $ 10.44 $ 9.90 $ 9.17      
Proceeds from Issuance of Common Stock $ 600,300 $ 341,600 $ 358,500 $ 1,362,747 $ 1,006,847 $ 235,275
Proceeds from Issuance of Common Stock, Net       1,300,000    
Payments of Stock Issuance Costs       $ 16,100