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
Jun. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis $ 93,826 $ 59,808
Unrealized Gain 10 18
Unrealized Loss (37) (7)
Fair Value 93,799 59,819
Money market funds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 2,177 5,886
Unrealized Gain      
Unrealized Loss      
Fair Value 2,177 5,886
Certificates of deposit [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 2,125 1,185
Unrealized Gain      
Unrealized Loss      
Fair Value 2,125 1,185
Corporate debt securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 56,231 20,237
Unrealized Gain 4 6
Unrealized Loss (31) (1)
Fair Value 56,204 20,242
U.S. Government securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 30,664 27,893
Unrealized Gain 6 12
Unrealized Loss (6) (6)
Fair Value 30,664 27,899
Municipal securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 1,419  
Unrealized Gain     
Unrealized Loss     
Fair Value 1,419  
Commercial paper [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 4,896 15,613
Unrealized Gain      
Unrealized Loss      
Fair Value 4,896 15,613
Marketable securities including cash equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 97,512 70,814
Unrealized Gain 10 18
Unrealized Loss (37) (7)
Fair Value 97,485 70,825
Less cash equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost Basis 3,686 11,006
Unrealized Gain      
Unrealized Loss      
Fair Value $ 3,686 $ 11,006