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Schedule of Debt Outstanding (Detail) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Debt Instrument [Line Items]    
Long-term debt $ 1,190,764 $ 1,245,014
Revolving Credit Facility
   
Debt Instrument [Line Items]    
Long-term debt 645,000 265,000
Senior Notes 6.25% Due 2013
   
Debt Instrument [Line Items]    
Long-term debt   375,000
Senior Notes 6.75% Due 2014
   
Debt Instrument [Line Items]    
Long-term debt 90,000 150,000
Senior Notes 7.75% Due 2017
   
Debt Instrument [Line Items]    
Long-term debt $ 455,764 $ 455,014