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Financial Instruments - Additional Information (Detail) (USD $)
 3 Months Ended
Mar. 31, 2014
Mar. 31, 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 $ (28,000) $ 1,000  
Revolving credit facility     70,000,000
Revolving credit facility maturity date Jun. 30, 2016    
Outstanding borrowings under the Credit Agreement 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