CASH, CASH EQUIVALENTS AND INVESTMENTS - Schedule of Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 99,929	$ 514,277
Available-for-sale Securities, Gross Unrealized Gains	67	190
Available-for-sale Securities, Gross Unrealized Losses		(6)
Available-for-sale Securities, Fair Value Disclosure	99,996	514,461
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		700
Available-for-sale Securities, Fair Value Disclosure		700
U.S. Government Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	99,929	513,577
Available-for-sale Securities, Gross Unrealized Gains	67	190
Available-for-sale Securities, Gross Unrealized Losses		(6)
Available-for-sale Securities, Fair Value Disclosure	$ 99,996	$ 513,761

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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Amortized cost of 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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