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Financial Instruments - Investments Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value $ 54,406 $ 38,966
Commercial paper [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 15,636  
Corporate bonds [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 5,436  
U.S. Treasury bills [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 17,254 31,592
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 1 [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value    31,592
Level 1 [Member] | Commercial paper [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
Level 1 [Member] | Corporate bonds [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
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 1 [Member] | Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
Level 2 [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 47,032   
Level 2 [Member] | Commercial paper [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 15,636  
Level 2 [Member] | Corporate bonds [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value 14,142  
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 17,254   
Level 2 [Member] | Municipal bond [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
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] | Commercial paper [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
Level 3 [Member] | Corporate bonds [Member]
    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]    
Total investments at fair value     
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      
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