Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments (Narrative) (Details)

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Derivative Financial Instruments (Narrative) (Details) (USD $)
1 Months Ended 12 Months Ended
Aug. 31, 2011
Oct. 31, 2009
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Derivative Financial Instruments [Abstract]          
Net reclassification from Accumulated comprehensive income to interest expense     $ 10,516,000 $ 6,900,000 $ 9,687,000
Estimated payment to be made under interest rate agreement     4,800,000    
Fair value of interest rate swap agreements     10,748,000 10,528,000  
Notional Amount     245,000,000    
Variable rate term notes 150,000,000 100,000,000      
Realized losses recognized in interest expense   $ 8,400,000 $ 5,500,000