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MARKETABLE SECURITIES Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Interest receivable	$ 1,000	$ 800
Amortized Cost	286,520	189,428
Gross Unrealized Gains	63	890
Gross Unrealized Losses	(77)	0
Estimated Fair Market Value	286,506	190,318
Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	82,364	63,506
Gross Unrealized Gains	12	44
Gross Unrealized Losses	(1)	0
Estimated Fair Market Value	82,375	63,550
Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,861	125,922
Gross Unrealized Gains	0	846
Gross Unrealized Losses	(4)	0
Estimated Fair Market Value	55,857	126,768
Investments due in 12 months or greater:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	148,295
Gross Unrealized Gains	51
Gross Unrealized Losses	(72)
Estimated Fair Market Value	148,274
Commercial paper | Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69,079	43,660
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	69,079	43,660
Commercial paper | Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,500
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	40,500
Corporate securities | Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13,285	19,846
Gross Unrealized Gains	12	44
Gross Unrealized Losses	(1)	0
Estimated Fair Market Value	13,296	19,890
Corporate securities | Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,361	125,922
Gross Unrealized Gains	0	846
Gross Unrealized Losses	(4)	0
Estimated Fair Market Value	15,357	$ 126,768
Corporate securities | Investments due in 12 months or greater:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	148,295
Gross Unrealized Gains	51
Gross Unrealized Losses	(72)
Estimated Fair Market Value	$ 148,274

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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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