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Financial Instruments - Additional Information (Detail) (USD $)
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
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 $ (36,000) $ 206,000 $ (41,000) $ 326,000
Revolving credit facility maturity date     Jan. 31, 2014  
Repayment of amount borrowed 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