MARKETABLE SECURITIES (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Debt securities, realized gain (loss)	$ 0	$ 0
Marketable securities	368,668,000	201,236,000
Debt securities, available-for-sale, realized gain			$ 100,000
Proceeds from the sale/maturity of marketable securities	162,755,000	114,526,000	$ 159,520,000
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Marketable securities	59,255,000	6,897,000
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities	299,413,000	164,297,000
Securities of government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Marketable securities	$ 10,000,000	$ 30,042,000

Amount of realized gain 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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

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- Definition

Amount of investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

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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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