Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Schedule of Fair Value of Derivatives Financial Instruments and Long-Term Senior Notes) (Detail)

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Fair Value Measurements (Schedule of Fair Value of Derivatives Financial Instruments and Long-Term Senior Notes) (Detail) (Level 2, USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Level 2
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Commodity derivatives, Assets $ 13,210 $ 4,087
8.50% Senior Notes, Assets      
Revolving bank credit facility, Assets      
Commodity derivatives, Liabilities   7,199
8.50% Senior Notes, Liabilities 616,500 612,000
Revolving bank credit facility, Liabilities $ 80,000 $ 117,000