Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail)

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Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis $ 57,178 $ 14,409
Unrealized Gain 21 2
Unrealized Loss (8) (3)
Fair Value 57,191 14,408
Money Market Funds [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 3,861 4,050
Unrealized Gain      
Unrealized Loss      
Fair Value 3,861 4,050
Certificate Of Deposits [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 485  
Unrealized Gain     
Unrealized Loss     
Fair Value 485  
Corporate Bonds [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 20,157 4,693
Unrealized Gain 11   
Unrealized Loss (8) (3)
Fair Value 20,160 4,690
U.S. Government Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 28,994 5,968
Unrealized Gain 10 2
Unrealized Loss      
Fair Value 29,004 5,970
Commercial Paper [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 12,315 5,548
Unrealized Gain 0   
Unrealized Loss      
Fair Value 12,315 5,548
Marketable Securities Including Cash Equivalents [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 65,812 20,259
Unrealized Gain 21 2
Unrealized Loss (8) (3)
Fair Value 65,825 20,258
Less Cash Equivalents [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis (8,634) (5,850)
Unrealized Gain      
Unrealized Loss      
Fair Value $ (8,634) $ (5,850)