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Short-Term and Long-Term Investments - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Unrealized Losses On Short Term And Long Term Investments [Line Items]        
Minimum period for which failed auction securities been in unrealized loss position 12 months 12 months    
Short Term Investments $ 50,166,000      
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 $ 2,517,000 2,510,000    
Gross Unrealized Losses 483,000 490,000    
Aggregate credit loss 33,000 $ 37,000 $ 41,000 $ 48,000
Aggregate temporary impairment loss $ 450,000