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Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost $ 192,602 $ 210,439
Cash, cash equivalents and short-term investments, Gross unrealized losses (111) (95)
Cash, cash equivalents and short-term investments, Fair market value 192,491 210,344
Cash and Cash Equivalents [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 80,304 73,551
Cash, cash equivalents and short-term investments, Fair market value 80,304 73,551
Short-term Investments [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 112,298 136,888
Cash, cash equivalents and short-term investments, Gross unrealized losses (111) (95)
Cash, cash equivalents and short-term investments, Fair market value 112,187 136,793
Cash and Money Market Funds [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 75,304 73,551
Cash, cash equivalents and short-term investments, Fair market value 75,304 73,551
Commercial Paper [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 48,936 2,997
Cash, cash equivalents and short-term investments, Gross unrealized losses (37)  
Cash, cash equivalents and short-term investments, Fair market value 48,899 2,997
Government and Government Agency Bonds [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 50,966 75,289
Cash, cash equivalents and short-term investments, Gross unrealized losses (48) (39)
Cash, cash equivalents and short-term investments, Fair market value 50,918 75,250
Corporate Bonds [Member]    
Cash and Cash Equivalents [Line Items]    
Cash, cash equivalents and short-term investments, Amortized cost 17,396 58,602
Cash, cash equivalents and short-term investments, Gross unrealized losses (26) (56)
Cash, cash equivalents and short-term investments, Fair market value $ 17,370 $ 58,546