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Financial Instruments - Investments Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2014
Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value $ 131,454 $ 38,966
Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 14,255 7,374
Non-governmental debt securities [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 98,737  
Treasury and federal agencies [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 18,462  
U.S. Treasury Bills [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value   31,592
Level 1 [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0 31,592
Level 1 [Member] | Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0 0
Level 1 [Member] | Non-governmental debt securities [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0  
Level 1 [Member] | Treasury and federal agencies [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0  
Level 1 [Member] | U.S. Treasury Bills [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value   31,592
Level 2 [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 124,080 0
Level 2 [Member] | Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 6,881 0
Level 2 [Member] | Non-governmental debt securities [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 98,737  
Level 2 [Member] | Treasury and federal agencies [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 18,462  
Level 2 [Member] | U.S. Treasury Bills [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value   0
Level 3 [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 7,374 7,374
Level 3 [Member] | Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 7,374 7,374
Level 3 [Member] | Non-governmental debt securities [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0  
Level 3 [Member] | Treasury and federal agencies [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 0  
Level 3 [Member] | U.S. Treasury Bills [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value   $ 0