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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 44,906	$ 107,767
Less Than 12 Months - Gross Unrealized Losses	(29)	(176)
12 Months or Longer - Estimated Fair Value	13,226	14,221
12 Months or Longer - Gross Unrealized Losses	(8)	(36)
Total - Estimated Fair Value	58,132	121,988
Total - Gross Unrealized Losses	(37)	(212)
Commercial paper (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	15,792	22,628
Less Than 12 Months - Gross Unrealized Losses	(19)	(29)
Total - Estimated Fair Value	15,792	22,628
Total - Gross Unrealized Losses	(19)	(29)
Corporate notes (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	27,115	66,557
Less Than 12 Months - Gross Unrealized Losses	(5)	(82)
12 Months or Longer - Estimated Fair Value	13,226	14,221
12 Months or Longer - Gross Unrealized Losses	(8)	(36)
Total - Estimated Fair Value	40,341	80,778
Total - Gross Unrealized Losses	(13)	(118)
Corporate notes (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	1,999	18,582
Less Than 12 Months - Gross Unrealized Losses	(5)	(65)
Total - Estimated Fair Value	1,999	18,582
Total - Gross Unrealized Losses	$ (5)	$ (65)

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount of accumulated unrealized loss on 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 12 months or longer.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrealized loss on 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 less than 12 months.

+ References

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

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