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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
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Available for sale securities with unrealized losses |  |
Less Than 12 Months - Estimated Fair Value | $ 17,863 | $ 107,767
Less Than 12 Months - Gross Unrealized Losses | (6) | (176)
12 Months or Longer - Estimated Fair Value | 4,400 | 14,221
12 Months or Longer - Gross Unrealized Losses | (1) | (36)
Total - Estimated Fair Value | 22,263 | 121,988
Total - Gross Unrealized Losses | (7) | (212)
Commercial paper (due in less than one year) |  |
Available for sale securities with unrealized losses |  |
Less Than 12 Months - Estimated Fair Value | 5,492 | 22,628
Less Than 12 Months - Gross Unrealized Losses | (1) | (29)
Total - Estimated Fair Value | 5,492 | 22,628
Total - Gross Unrealized Losses | (1) | (29)
Corporate notes (due in less than one year) |  |
Available for sale securities with unrealized losses |  |
Less Than 12 Months - Estimated Fair Value | 11,318 | 66,557
Less Than 12 Months - Gross Unrealized Losses | (4) | (82)
12 Months or Longer - Estimated Fair Value | 4,400 | 14,221
12 Months or Longer - Gross Unrealized Losses | (1) | (36)
Total - Estimated Fair Value | 15,718 | 80,778
Total - Gross Unrealized Losses | (5) | (118)
Corporate notes (due in one to two years) |  |
Available for sale securities with unrealized losses |  |
Less Than 12 Months - Estimated Fair Value | 1,053 | 18,582
Less Than 12 Months - Gross Unrealized Losses | (1) | (65)
Total - Estimated Fair Value | 1,053 | 18,582
Total - Gross Unrealized Losses | $ (1) | $ (65)

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