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 [Member], USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Level 2 [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Commodity derivatives   $ 4,087
Commodity derivatives 10,573 7,199
8.50% Senior Notes 648,000 612,000
Revolving bank credit facility $ 119,000 $ 117,000