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Fair Value Measurements - Additional Information (Detail) (USD $)
9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Number of bonds received 2  
Total Debt $ 1,148,461,000 $ 1,073,825,000
Bonds Series A and Series B [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Number of bonds received 2  
Bonds A Series [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivables, carrying value 88,900,000  
Maturity date of notes receivable Jul. 01, 2034  
Bonds B Series [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivables, carrying value 57,500,000  
Maturity date of notes receivable Sep. 01, 2037  
Notes receivable, fair value 38,000,000  
3.75% Convertible Senior Notes [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Face amount of outstanding debt 360,000,000  
Interest rate of Senior Notes 3.75%  
Total Debt 329,446,000 319,246,000
Fair value of the convertible notes 341,000,000  
Maturity year of note 2014  
6.75% Senior Notes [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Interest rate of Senior Notes 6.75%  
Total Debt 152,180,000 152,180,000
Maturity year of note 2014  
Fair value of senior notes $ 152,200,000