CASH, CASH EQUIVALENTS AND INVESTMENTS - Schedule of Cash, Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	$ 726,285	$ 630,010
Cash Equivalents, Gross Unrealized Gains		6
Cash Equivalents, Gross Unrealized Losses	(6)	(4)
Cash and Cash Equivalents, Fair Value Disclosure	726,279	630,012
Cash Accounts in Banking Institutions [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	160,850	163,779
Cash and Cash Equivalents, Fair Value Disclosure	160,850	163,779
Money Market Accounts [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	16,438	17,261
Cash and Cash Equivalents, Fair Value Disclosure	16,438	17,261
U.S. Government Bonds [Member]
Cash And Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	548,997	448,970
Cash Equivalents, Gross Unrealized Gains		6
Cash Equivalents, Gross Unrealized Losses	(6)	(4)
Cash and Cash Equivalents, Fair Value Disclosure	$ 548,991	$ 448,972