INVESTMENTS AND FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investments And Fair Value Disclosures [Line Items]
Amortized Cost		$ 587,561
Gross Unrealized Gains		0
Gross Unrealized Losses		(730)
Fair Value		586,831
Cash Equivalents [Member]
Investments And Fair Value Disclosures [Line Items]
Amortized Cost		576,761
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		576,761
Auction Rate Securities [Member]
Investments And Fair Value Disclosures [Line Items]
Amortized Cost		10,800
Gross Unrealized Gains		0
Gross Unrealized Losses		(730)
Fair Value		10,070
Fair Value, Inputs, Level 1 [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		576,761
Fair Value, Inputs, Level 1 [Member] \| Cash Equivalents [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure	$ 3,252,000	576,761
Fair Value, Inputs, Level 1 [Member] \| Auction Rate Securities [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		0
Fair Value, Inputs, Level 2 [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		0
Fair Value, Inputs, Level 2 [Member] \| Auction Rate Securities [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		0
Fair Value, Inputs, Level 3 [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		10,070
Fair Value, Inputs, Level 3 [Member] \| Auction Rate Securities [Member]
Investments And Fair Value Disclosures [Line Items]
Assets, fair value disclosure		$ 10,070

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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).

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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).

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