FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	$ 46,277	$ 107,767
Less Than 12 Months - Gross Unrealized Losses	(25)	(176)
12 Months or Greater - Estimated Fair Value		14,221
12 Months or Greater - Gross Unrealized Losses		(36)
Total - Estimated Fair Value	46,277	121,988
Total - Gross Unrealized Losses	(25)	(212)
Commercial paper (due in less than one year)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	8,571	22,628
Less Than 12 Months - Gross Unrealized Losses	(3)	(29)
Total - Estimated Fair Value	8,571	22,628
Total - Gross Unrealized Losses	(3)	(29)
Corporate notes (due in less than one year)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	26,082	66,557
Less Than 12 Months - Gross Unrealized Losses	(13)	(82)
12 Months or Greater - Estimated Fair Value		14,221
12 Months or Greater - Gross Unrealized Losses		(36)
Total - Estimated Fair Value	26,082	80,778
Total - Gross Unrealized Losses	(13)	(118)
Corporate notes (due in one to two years)
Schedule Of Available For Sale Securities [Line Items]
Less Than 12 Months - Estimated Fair Value	11,624	18,582
Less Than 12 Months - Gross Unrealized Losses	(9)	(65)
Total - Estimated Fair Value	11,624	18,582
Total - Gross Unrealized Losses	$ (9)	$ (65)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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