FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	$ 53,595	$ 46,277
Less Than 12 Months - Gross Unrealized Losses	(13)	(25)
Total - Estimated Fair Value	53,595	46,277
Total - Gross Unrealized Losses	(13)	(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	5,999
Less Than 12 Months - Gross Unrealized Losses	(1)
Total - Estimated Fair Value	5,999
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	16,981	8,571
Less Than 12 Months - Gross Unrealized Losses	(2)	(3)
Total - Estimated Fair Value	16,981	8,571
Total - Gross Unrealized Losses	(2)	(3)
Corporate notes (due in less than one year)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	20,096	26,082
Less Than 12 Months - Gross Unrealized Losses	(5)	(13)
Total - Estimated Fair Value	20,096	26,082
Total - Gross Unrealized Losses	(5)	(13)
Corporate notes (due in one to two years)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	10,519	11,624
Less Than 12 Months - Gross Unrealized Losses	(5)	(9)
Total - Estimated Fair Value	10,519	11,624
Total - Gross Unrealized Losses	$ (5)	$ (9)