Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Composition of Financial Instruments (Detail)

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Financial Instruments - Composition of Financial Instruments (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 63,087 $ 72,102
Gross unrealized gains 23 10
Gross unrealized losses (4) (30)
Fair Value 63,106 72,082
Government debt securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,999 15,966
Gross unrealized gains 3 3
Gross unrealized losses      
Fair Value 3,002 15,969
Corporate debt securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 50,393 41,764
Gross unrealized gains 20 7
Gross unrealized losses (4) (30)
Fair Value 50,409 41,741
Money market funds [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 9,695 14,372
Gross unrealized gains      
Gross unrealized losses      
Fair Value 9,695 14,372
Cash and cash equivalents [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost (9,695) (14,372)
Gross unrealized gains      
Gross unrealized losses      
Fair Value (9,695) (14,372)
Investments [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 53,392 57,730
Gross unrealized gains 23 10
Gross unrealized losses (4) (30)
Fair Value $ 53,411 $ 57,710