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Debt and Credit Arrangements Convertible Securities Conversion Rates (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Debt Instrument      
Convertible Notes, terms of conversion feature convertible at any time if the average price of our common stock for 20 trading days immediately preceding the conversion date is greater than or equal to a specified percentage of the conversion price; this percentage was equal to 116.0% in 2011 and declines 0.5% each year until it reaches 110% at maturity    
Convertible Notes, earliest convertible date February 15, 2023    
Convertible Notes, latest convertible date March 15, 2023    
Convertible Notes, conversion price $ 12.13 $ 12.42 $ 12.42
Convertible Notes, conversion rate per note 82.4612 80.5153 80.5153