Annual report pursuant to Section 13 and 15(d)

Schedule of Long-Term Debt (Detail)

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Schedule of Long-Term Debt (Detail) (USD $)
Dec. 31, 2012
Oct. 24, 2012
Dec. 31, 2011
Jun. 10, 2011
Debt Instrument [Line Items]        
Debt premiums, net of amortization $ 17,611,000      
Total long-term debt 1,087,611,000 [1]   717,000,000 [1]  
Current maturities of long-term debt          
Long-term debt, less current maturities 1,087,611,000   717,000,000  
8.50% Senior Notes, due June 2019
       
Debt Instrument [Line Items]        
Long-term Debt unsecured 900,000,000 300,000,000 600,000,000 600,000,000
Revolving Bank Credit Facility Due May 2015
       
Debt Instrument [Line Items]        
Long-term debt secured $ 170,000,000   $ 117,000,000  
[1] Aggregate annual maturities of long-term debt as of December 31, 2012 are as follows (in millions): 2013 - $0.0; 2014 - $0.0; 2015 - $170.0; 2016 - $0.0; thereafter - $900.0.