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Fair Value of Financial Instruments (Details Textual) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Fair value of financial instruments (Textual) [Abstract]    
Percentage of aggregate principal amount of outstanding 5.375% 5.375%
5.375% Fixed Rate Debt [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Amount of fixed rate debt 250.0 250.0