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FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Current Available-for-Sale Marketable Debt Securities (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Amortized Cost | $ 49,995,000 |  |
Gross Unrealized Gains | 0 |  |
Gross Unrealized Losses | 0 |  |
Fair Value | 49,995,000 | $ 0 |
Proceeds from maturities of marketable debt securities | 50,000,000 | 25,000,000 | $ 35,000,000
Gross realized gains (losses) from the maturities of available-for-sale marketable debt securities | 0 | $ 0 |
Treasury discount notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Amortized Cost | 49,995,000 |  |
Gross Unrealized Gains | 0 |  |
Gross Unrealized Losses | 0 |  |
Fair Value | $ 49,995,000 |  |

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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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- Definition 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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- Definition 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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 + Details
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