FINANCIAL INSTRUMENTS - Current Available-for-Sale Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 123,246	$ 4,995
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(3)	0
Fair Value	123,246	4,995
Treasury discount notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	112,291
Gross Unrealized Gains	3
Gross Unrealized Losses	(3)
Fair Value	112,291
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,955	4,995
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 10,955	$ 4,995

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
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-SubTopic 10
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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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), classified as current.

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-Publisher FASB
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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