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Long-Term Investments - Additional Information (Detail) - USD ($)
 9 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Sep. 30, 2015
Dec. 31, 2014
Unrealized Losses On Short Term And Long Term Investments [Line Items]        
Amortized cost of securities   $ 3,340,000    
Minimum period for which failed auction securities been in unrealized loss position 12 months      
Estimated Fair Value   2,866,000    
Gross unrealized losses   474,000    
Aggregate credit loss $ 62,000 72,000 $ 72,000 $ 84,000
Failed Auction Security [Member]        
Unrealized Losses On Short Term And Long Term Investments [Line Items]        
Amortized cost of securities $ 3,000,000 3,000,000    
Period for which failed auction securities been in unrealized loss position Exceeds 12 months      
Estimated Fair Value $ 2,580,000 2,526,000    
Gross unrealized losses 420,000 $ 474,000    
Aggregate credit loss 62,000      
Aggregate temporary impairment loss $ 358,000