INVESTMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale
Amortized Cost	$ 1,252,346	$ 925,559
Gross Unrealized Holding Gains	41	165
Gross Unrealized Holding Losses	66	79
Fair Value	1,252,321	925,645
Continuous Unrealized Loss Position less than 12 Months	66	79
Short-term \| Commercial paper
Available-for-sale
Amortized Cost	292,094	119,886
Fair Value	292,094	119,886
Short-term \| Certificates of deposit
Available-for-sale
Amortized Cost	47,616	20,387
Fair Value	47,616	20,387
Short-term \| Municipal securities
Available-for-sale
Amortized Cost		9,083
Fair Value		9,083
Short-term \| U.S. government agency securities
Available-for-sale
Amortized Cost	70,202	81,521
Gross Unrealized Holding Gains	10	13
Gross Unrealized Holding Losses	2	3
Fair Value	70,210	81,531
Continuous Unrealized Loss Position less than 12 Months	2	3
Short-term \| U.S. treasuries
Available-for-sale
Amortized Cost	814,178	650,386
Gross Unrealized Holding Gains	30	150
Gross Unrealized Holding Losses	62	69
Fair Value	814,146	650,467
Continuous Unrealized Loss Position less than 12 Months	62	69
Long-term \| U.S. government agency securities
Available-for-sale
Amortized Cost	1,416	10,350
Gross Unrealized Holding Gains		1
Fair Value	1,416	10,351
Long-term \| U.S. treasuries
Available-for-sale
Amortized Cost	26,840	33,946
Gross Unrealized Holding Gains	1	1
Gross Unrealized Holding Losses	2	7
Fair Value	26,839	33,940
Continuous Unrealized Loss Position less than 12 Months	$ 2	$ 7

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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