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Cash, Cash Equivalents and Investments - Components of Cash, Cash Equivalents and Investments (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]        
Cash $ 34,986 $ 36,404    
Cash equivalents 5,098      
Money market instruments 5,076 1,699    
Cash and cash equivalents 45,160 38,103 33,203 119,831
Short-term investments 105,105 144,431    
Limited partnership interest (accounted for using cost method) 3,740 5,933    
Long-term investments 238,255 174,906    
Total 388,520 357,440    
Corporate Bonds [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 46,001 55,570    
Long-term investments 100,072 59,902    
Asset-Backed Securities [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 17,666      
Long-term investments 34,710      
Municipal Bonds [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 16,224 54,036    
Long-term investments 17,846 69,680    
Agency Bonds [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 7,482 27,545    
Long-term investments 29,441 12,335    
Treasury Bills [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 5,997 1,945    
Long-term investments 36,276      
Covered Bonds [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 5,618 1,319    
Long-term investments 5,564 4,701    
Sovereign Bonds [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments 3,986 4,016    
Long-term investments 10,606 22,355    
Corporate Stock [Member]
        
Schedule of Available-for-sale Securities [Line Items]        
Short-term investments $ 2,131