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Financial Instruments - Investments Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value $ 59,592 $ 71,258
U.S. Treasury bills [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value 52,210 63,876
Municipal bond [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value 7,382 7,382
Level 1 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value 52,210 63,876
Level 1 [Member] | U.S. Treasury bills [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value 52,210 63,876
Level 1 [Member] | Municipal bond [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value     
Level 2 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value      
Level 2 [Member] | U.S. Treasury bills [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value      
Level 2 [Member] | Municipal bond [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value      
Level 3 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value 7,382 7,382
Level 3 [Member] | U.S. Treasury bills [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value     
Level 3 [Member] | Municipal bond [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total investments at fair value $ 7,382 $ 7,382