CASH, CASH EQUIVALENTS AND INVESTMENTS - Schedule of Cash, Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	$ 630,010	$ 131,627
Cash Equivalents, Gross Unrealized Gains	6
Cash Equivalents, Gross Unrealized Losses	(4)
Cash and Cash Equivalents, Fair Value Disclosure	630,012	131,627
Cash Accounts in Banking Institutions [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	163,779	119,272
Cash and Cash Equivalents, Fair Value Disclosure	163,779	119,272
Money Market Accounts [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	17,261	12,355
Cash and Cash Equivalents, Fair Value Disclosure	17,261	$ 12,355
U.S. Government Bonds [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	448,970
Cash Equivalents, Gross Unrealized Gains	6
Cash Equivalents, Gross Unrealized Losses	(4)
Cash and Cash Equivalents, Fair Value Disclosure	$ 448,972