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Summary of Cash, Cash Equivalents and Marketable Securities Available-for-sale (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost $ 76,452 $ 125,085
Unrealized Gains 22 46
Unrealized Losses   (1)
Estimated Fair Value 76,474 125,130
Cash and Cash Equivalents
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 12,191 7,599
Estimated Fair Value 12,191 7,599
Cash and Cash Equivalents | Cash
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 2,093 1,542
Estimated Fair Value 2,093 1,542
Cash and Cash Equivalents | Money market funds
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 9,598 3,140
Estimated Fair Value 9,598 3,140
Cash and Cash Equivalents | Municipal Securities
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost   2,202
Estimated Fair Value   2,202
Cash and Cash Equivalents | US Government Agencies Debt Securities
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 500 715
Estimated Fair Value 500 715
Available-for-sale Securities
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 64,261 117,486
Unrealized Gains 22 46
Unrealized Losses   (1)
Estimated Fair Value 64,283 117,531
Available-for-sale Securities | US Government Agencies Debt Securities
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 61,761 116,986
Unrealized Gains 22 46
Unrealized Losses   (1)
Estimated Fair Value 61,783 117,031
Available-for-sale Securities | US Treasury Securities
    
Cash Cash Equivalents And Marketable Securities [Line Items]    
Amortized Cost 2,500 500
Estimated Fair Value $ 2,500 $ 500