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Fair Value Measurements - Additional Information (Detail) (USD $)
Mar. 31, 2013
Contract
Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Number of bonds received 2  
Total Debt $ 1,092,081,000 $ 1,031,863,000
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 336,631,000 333,039,000
Fair value of the convertible notes 354,000,000  
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 60,000,000  
Maturity date of notes receivable Sep. 01, 2037  
Notes receivable, fair value $ 41,000,000