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Short-Term and Long-Term Investments - Additional Information (Detail) - USD ($)
 6 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Jun. 30, 2020
Dec. 31, 2019
Unrealized Losses On Short Term And Long Term Investments [Line Items]        
Short Term Investments $ 70,469,000 $ 50,166,000    
Minimum period for which failed auction securities been in unrealized loss position 12 months      
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 $ 2,561,000 2,517,000    
Gross Unrealized Losses 439,000 483,000    
Aggregate credit loss 31,000 $ 33,000 $ 35,000 $ 37,000
Aggregate temporary impairment loss $ 408,000