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Short-Term and Long-Term Investments - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturities (Detail)
$ in Thousands
Dec. 31, 2020
USD ($)
Schedule of Available-for-sale Securities [Line Items]  
Debt Securities, Available-for-sale, Amortized Cost $ 70,172
Available For Sale Debt Securities Estimated Fair Value 70,164
Failed Auction Security [Member]  
Schedule of Available-for-sale Securities [Line Items]  
Due in twenty to forty years, Cost 3,000
Due in twenty to forty years, Estimated Fair Value 2,517
US Treasury Obligations [Member]  
Schedule of Available-for-sale Securities [Line Items]  
Maturities greater than three months but less than one year, Cost 50,174
Maturities greater than three months but less than one year, Estimated Fair Value 50,166
Maturities less than three months, Cost 19,998
Maturities less than three months, Estimated Fair Value $ 19,998