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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]    
Less Than 12 Months - Estimated Fair Value $ 56,850 $ 46,277
Less Than 12 Months - Gross Unrealized Losses (33) (25)
Total - Estimated Fair Value 56,850 46,277
Total - Gross Unrealized Losses (33) (25)
Government-sponsored enterprise securities (due in one to two years)    
Schedule Of Available For Sale Securities [Line Items]    
Less Than 12 Months - Estimated Fair Value 4,999  
Less Than 12 Months - Gross Unrealized Losses (1)  
Total - Estimated Fair Value 4,999  
Total - Gross Unrealized Losses (1)  
Commercial paper (due in less than one year)    
Schedule Of Available For Sale Securities [Line Items]    
Less Than 12 Months - Estimated Fair Value 22,956 8,571
Less Than 12 Months - Gross Unrealized Losses (8) (3)
Total - Estimated Fair Value 22,956 8,571
Total - Gross Unrealized Losses (8) (3)
Corporate notes (due in less than one year)    
Schedule Of Available For Sale Securities [Line Items]    
Less Than 12 Months - Estimated Fair Value 12,573 26,082
Less Than 12 Months - Gross Unrealized Losses (7) (13)
Total - Estimated Fair Value 12,573 26,082
Total - Gross Unrealized Losses (7) (13)
Corporate notes (due in one to two years)    
Schedule Of Available For Sale Securities [Line Items]    
Less Than 12 Months - Estimated Fair Value 16,322 11,624
Less Than 12 Months - Gross Unrealized Losses (17) (9)
Total - Estimated Fair Value 16,322 11,624
Total - Gross Unrealized Losses $ (17) $ (9)