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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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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)

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