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Fair Value Measurement of Assets and Liabilities - Summary of Company's Financial Instruments, Fair Value on a Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
    
Cash equivalents    
Total cash equivalents $ 2,255 $ 3,476
Available-for-sale:    
Total short-term marketable securities 24,432 38,064
Total long-term marketable securities 5,316 1,201
Total financial assets 32,003 42,741
Fair Value, Measurements, Recurring [Member] | Government agency securities [Member]
    
Available-for-sale:    
Total short-term marketable securities 3,353 3,266
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 5,877 11,260
Fair Value, Measurements, Recurring [Member] | Certificates of deposit [Member]
    
Available-for-sale:    
Total short-term marketable securities 5,001 6,205
Total long-term marketable securities 2,740 1,201
Fair Value, Measurements, Recurring [Member] | Corporate debentures / bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 10,201 17,333
Total long-term marketable securities 2,576  
Fair Value, Measurements, Recurring [Member] | Money market funds [Member]
    
Cash equivalents    
Total cash equivalents 47 47
Fair Value, Measurements, Recurring [Member] | US Treasury securities [Member]
    
Cash equivalents    
Total cash equivalents 2,208 3,429
Level 1 [Member]
    
Cash equivalents    
Total cash equivalents 47 47
Available-for-sale:    
Total short-term marketable securities 0 0
Total long-term marketable securities 0 0
Total financial assets 47 47
Level 1 [Member] | Government agency securities [Member]
    
Available-for-sale:    
Total short-term marketable securities 0 0
Level 1 [Member] | Municipal bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 0 0
Level 1 [Member] | Certificates of deposit [Member]
    
Available-for-sale:    
Total short-term marketable securities 0 0
Total long-term marketable securities 0 0
Level 1 [Member] | Corporate debentures / bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 0 0
Total long-term marketable securities 0  
Level 1 [Member] | Money market funds [Member]
    
Cash equivalents    
Total cash equivalents 47 47
Level 1 [Member] | US Treasury securities [Member]
    
Cash equivalents    
Total cash equivalents 0 0
Level 2 [Member]
    
Cash equivalents    
Total cash equivalents 2,208 3,429
Available-for-sale:    
Total short-term marketable securities 24,432 38,064
Total long-term marketable securities 5,316 1,201
Total financial assets 31,956 42,694
Level 2 [Member] | Government agency securities [Member]
    
Available-for-sale:    
Total short-term marketable securities 3,353 3,266
Level 2 [Member] | Municipal bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 5,877 11,260
Level 2 [Member] | Certificates of deposit [Member]
    
Available-for-sale:    
Total short-term marketable securities 5,001 6,205
Total long-term marketable securities 2,740 1,201
Level 2 [Member] | Corporate debentures / bonds [Member]
    
Available-for-sale:    
Total short-term marketable securities 10,201 17,333
Total long-term marketable securities 2,576  
Level 2 [Member] | Money market funds [Member]
    
Cash equivalents    
Total cash equivalents 0 0
Level 2 [Member] | US Treasury securities [Member]
    
Cash equivalents    
Total cash equivalents $ 2,208 $ 3,429