MARKETABLE SECURITIES - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale securities
Amortized Cost	$ 762,764	$ 175,082
Gains in Accumulated Other Comprehensive Income (Loss)	1,492	12
Losses in Accumulated Other Comprehensive Income (Loss)	(3)	(87)
Marketable securities	764,253	175,007
Cash equivalents
Available-for-sale securities
Amortized Cost	246,905	30,320
Gains in Accumulated Other Comprehensive Income (Loss)	4	2
Losses in Accumulated Other Comprehensive Income (Loss)	(2)	0
Marketable securities	246,907	30,322
Marketable securities
Available-for-sale securities
Amortized Cost	515,859	144,762
Gains in Accumulated Other Comprehensive Income (Loss)	1,488	10
Losses in Accumulated Other Comprehensive Income (Loss)	(1)	(87)
Marketable securities	517,346	144,685
U.S. government agency securities \| Cash equivalents
Available-for-sale securities
Amortized Cost	246,905	30,320
Gains in Accumulated Other Comprehensive Income (Loss)	4	2
Losses in Accumulated Other Comprehensive Income (Loss)	(2)	0
Marketable securities	246,907	30,322
U.S. government agency securities \| Marketable securities
Available-for-sale securities
Amortized Cost	256,425	140,745
Gains in Accumulated Other Comprehensive Income (Loss)	102	10
Losses in Accumulated Other Comprehensive Income (Loss)	(1)	(73)
Marketable securities	256,526	140,682
Corporate bonds \| Marketable securities
Available-for-sale securities
Amortized Cost	219,264	4,017
Gains in Accumulated Other Comprehensive Income (Loss)	1,297	0
Losses in Accumulated Other Comprehensive Income (Loss)	0	(14)
Marketable securities	220,561	$ 4,003
Certificates of deposit \| Marketable securities
Available-for-sale securities
Amortized Cost	10,000
Gains in Accumulated Other Comprehensive Income (Loss)	0
Losses in Accumulated Other Comprehensive Income (Loss)	0
Marketable securities	10,000
Commercial paper \| Marketable securities
Available-for-sale securities
Amortized Cost	7,996
Gains in Accumulated Other Comprehensive Income (Loss)	4
Losses in Accumulated Other Comprehensive Income (Loss)	0
Marketable securities	8,000
Asset backed securities \| Marketable securities
Available-for-sale securities
Amortized Cost	22,174
Gains in Accumulated Other Comprehensive Income (Loss)	85
Losses in Accumulated Other Comprehensive Income (Loss)	0
Marketable securities	$ 22,259

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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