Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) (USD $)
In Millions, except Share data, unless otherwise specified
0 Months Ended 12 Months Ended
Oct. 05, 2009
Dec. 31, 2011
Dec. 31, 2009
Sep. 14, 2011
Shareholders' Equity [Abstract]        
Common stock value authorized under equity offering program       $ 125
Common stock shares issued under equity offering program 4,025,000 1,166,875 1,430,521  
Weighted average issue price of common stock $ 29.75 $ 40.59    
Proceeds from issuance of common stock   46.4 32.6  
Offering related costs and commissions 114.0 0.9    
Expenses related to equity program   0.4    
Common stock, value reserved for future issuance   $ 77.6