MARKETABLE SECURITIES Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Interest receivable	$ 1,200	$ 800
Amortized Cost	147,757	189,428
Gross Unrealized Gains	310	890
Gross Unrealized Losses	0	0
Estimated Fair Market Value	148,067	190,318
Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	96,675	63,506
Gross Unrealized Gains	107	44
Gross Unrealized Losses	0	0
Estimated Fair Market Value	96,782	63,550
Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51,082	125,922
Gross Unrealized Gains	203	846
Gross Unrealized Losses	0	0
Estimated Fair Market Value	51,285	126,768
Commercial paper \| Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,999	43,660
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	1,999	43,660
Commercial paper \| Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,983
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	19,983
Corporate securities \| Investments due in 3 months or less:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	94,676	19,846
Gross Unrealized Gains	107	44
Gross Unrealized Losses	0	0
Estimated Fair Market Value	94,783	19,890
Corporate securities \| Investments due in 4-12 months:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,099	125,922
Gross Unrealized Gains	203	846
Gross Unrealized Losses	0	0
Estimated Fair Market Value	$ 31,302	$ 126,768

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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