Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

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Fair Value Measurements (Details) (Level 2 [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2012
Dec. 31, 2011
Level 2 [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivatives, Assets    $ 4,087
Derivatives, Liabilities 36,946 7,199
8.50% Senior Notes, Assets      
8.50% Senior Notes, Liabilities 633,000 612,000
Revolving bank credit facility, Assets      
Revolving bank credit facility, Liabilities $ 84,000 $ 117,000