MARKETABLE SECURITIES - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale securities
Amortized Cost	$ 939,182	$ 936,476
Gains in Accumulated Other Comprehensive Income (Loss)	343	696
Losses in Accumulated Other Comprehensive Income (Loss)	(276)	0
Estimated Fair Value	939,249	937,172
Cash equivalents
Available-for-sale securities
Amortized Cost	2,917	589,986
Gains in Accumulated Other Comprehensive Income (Loss)	1	8
Losses in Accumulated Other Comprehensive Income (Loss)	0	0
Estimated Fair Value	2,918	589,994
Marketable securities
Available-for-sale securities
Amortized Cost	936,265	346,490
Gains in Accumulated Other Comprehensive Income (Loss)	342	688
Losses in Accumulated Other Comprehensive Income (Loss)	(276)	0
Estimated Fair Value	936,331	347,178
Corporate bonds \| Cash equivalents
Available-for-sale securities
Amortized Cost	2,917
Gains in Accumulated Other Comprehensive Income (Loss)	1
Losses in Accumulated Other Comprehensive Income (Loss)	0
Estimated Fair Value	2,918
Corporate bonds \| Marketable securities
Available-for-sale securities
Amortized Cost	376,516	132,301
Gains in Accumulated Other Comprehensive Income (Loss)	262	612
Losses in Accumulated Other Comprehensive Income (Loss)	(80)	0
Estimated Fair Value	376,698	132,913
U.S. government agency securities \| Cash equivalents
Available-for-sale securities
Amortized Cost		589,986
Gains in Accumulated Other Comprehensive Income (Loss)		8
Losses in Accumulated Other Comprehensive Income (Loss)		0
Estimated Fair Value		589,994
U.S. government agency securities \| Marketable securities
Available-for-sale securities
Amortized Cost	276,227	207,119
Gains in Accumulated Other Comprehensive Income (Loss)	29	52
Losses in Accumulated Other Comprehensive Income (Loss)	(186)	0
Estimated Fair Value	276,070	207,171
Asset backed securities \| Marketable securities
Available-for-sale securities
Amortized Cost	55,660	7,070
Gains in Accumulated Other Comprehensive Income (Loss)	9	24
Losses in Accumulated Other Comprehensive Income (Loss)	(9)	0
Estimated Fair Value	55,660	$ 7,094
Certificates of deposit \| Marketable securities
Available-for-sale securities
Amortized Cost	212,863
Gains in Accumulated Other Comprehensive Income (Loss)	41
Losses in Accumulated Other Comprehensive Income (Loss)	(1)
Estimated Fair Value	212,903
Commercial paper \| Marketable securities
Available-for-sale securities
Amortized Cost	14,999
Gains in Accumulated Other Comprehensive Income (Loss)	1
Losses in Accumulated Other Comprehensive Income (Loss)	0
Estimated Fair Value	$ 15,000

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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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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