INVESTMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale
Amortized Cost	$ 1,060,060	$ 925,559
Gross Unrealized Holding Gains	47	165
Gross Unrealized Holding Losses	122	79
Fair Value	1,059,985	925,645
Continuous Unrealized Loss Position less than 12 Months	122	79
Short-term \| Commercial paper
Available-for-sale
Amortized Cost	186,912	119,886
Fair Value	186,912	119,886
Short-term \| Certificates of deposit
Available-for-sale
Amortized Cost	43,240	20,387
Gross Unrealized Holding Gains	2
Fair Value	43,242	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	64,914	81,521
Gross Unrealized Holding Gains	10	13
Gross Unrealized Holding Losses	2	3
Fair Value	64,922	81,531
Continuous Unrealized Loss Position less than 12 Months	2	3
Short-term \| U.S. treasuries
Available-for-sale
Amortized Cost	673,912	650,386
Gross Unrealized Holding Gains	35	150
Gross Unrealized Holding Losses	71	69
Fair Value	673,876	650,467
Continuous Unrealized Loss Position less than 12 Months	71	69
Long-term \| U.S. government agency securities
Available-for-sale
Amortized Cost	29,659	10,350
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses	8
Fair Value	29,651	10,351
Continuous Unrealized Loss Position less than 12 Months	8
Long-term \| U.S. treasuries
Available-for-sale
Amortized Cost	61,423	33,946
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses	41	7
Fair Value	61,382	33,940
Continuous Unrealized Loss Position less than 12 Months	$ 41	$ 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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