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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

X

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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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