FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	$ 127,285	$ 46,277
Less Than 12 Months - Gross Unrealized Losses	(73)	(25)
Total - Estimated Fair Value	127,285	46,277
Total - Gross Unrealized Losses	(73)	(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	6,500
Less Than 12 Months - Gross Unrealized Losses	(1)
Total - Estimated Fair Value	6,500
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	51,103	8,571
Less Than 12 Months - Gross Unrealized Losses	(31)	(3)
Total - Estimated Fair Value	51,103	8,571
Total - Gross Unrealized Losses	(31)	(3)
Corporate notes (due in less than one year)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	38,362	26,082
Less Than 12 Months - Gross Unrealized Losses	(18)	(13)
Total - Estimated Fair Value	38,362	26,082
Total - Gross Unrealized Losses	(18)	(13)
Corporate notes (due in one to two years)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	31,320	11,624
Less Than 12 Months - Gross Unrealized Losses	(23)	(9)
Total - Estimated Fair Value	31,320	11,624
Total - Gross Unrealized Losses	$ (23)	$ (9)