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, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis $ 87,876 $ 59,808
Unrealized Gain 43 18
Unrealized Loss (6) (7)
Fair Value 87,913 59,819
Money market funds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 4,001 5,886
Unrealized Gain      
Unrealized Loss      
Fair Value 4,001 5,886
Certificates of deposit [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 1,880 1,185
Unrealized Gain      
Unrealized Loss      
Fair Value 1,880 1,185
Corporate debt securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 56,466 20,237
Unrealized Gain 23 6
Unrealized Loss (5) (1)
Fair Value 56,484 20,242
U.S. Government securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 26,071 27,893
Unrealized Gain 19 12
Unrealized Loss (1) (6)
Fair Value 26,089 27,899
Municipal securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 1,210  
Unrealized Gain 1  
Unrealized Loss     
Fair Value 1,211  
Commercial paper [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 2,249 15,613
Unrealized Gain      
Unrealized Loss      
Fair Value 2,249 15,613
Marketable securities including cash equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 91,877 70,814
Unrealized Gain 43 18
Unrealized Loss (6) (7)
Fair Value 91,914 70,825
Less cash equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 4,001 11,006
Unrealized Gain      
Unrealized Loss      
Fair Value $ 4,001 $ 11,006