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Financial Instruments - Additional Information (Detail) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Financial Instruments [Line Items]          
Period cash equivalents and short-term investments have been in continuous unrealized loss position, years, maximum     1 year    
Period cash equivalents and long-term investments have been in continuous unrealized loss position, years, minimum     1 year    
Cumulative unrealized income (loss) on municipal bonds $ (108,000) $ 36,000 $ (243,000) $ 41,000  
Revolving credit facility         70,000,000
Revolving credit facility maturity date     Jun. 30, 2016    
Outstanding borrowings under the Credit Agreement 0   0    
Municipal Bond [Member]
         
Financial Instruments [Line Items]          
Period debt obligations mature, years, maximum     1 year    
Cumulative unrealized income (loss) on municipal bonds     $ (500,000)