INVESTMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Available-for-sale
Amortized Cost	$ 1,482,934	$ 1,429,600
Gross Unrealized Holding Gains	41	101
Gross Unrealized Holding Losses	3,488	5,944
Fair Value	1,479,487	1,423,757
Continuous Unrealized Loss Position less than 12 Months	3,488	5,944
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | Commercial paper
Available-for-sale
Amortized Cost	329,770	197,712
Gross Unrealized Holding Gains	0	1
Gross Unrealized Holding Losses	2	4
Fair Value	329,768	197,709
Continuous Unrealized Loss Position less than 12 Months	2	4
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | Certificates of deposit
Available-for-sale
Amortized Cost	15,161	10,078
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair Value	15,161	10,078
Continuous Unrealized Loss Position less than 12 Months	0	0
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | Municipal securities
Available-for-sale
Amortized Cost	59,158	211,791
Gross Unrealized Holding Gains	0	60
Gross Unrealized Holding Losses	125	612
Fair Value	59,033	211,239
Continuous Unrealized Loss Position less than 12 Months	125	612
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | U.S. government agency securities
Available-for-sale
Amortized Cost	152,071	109,697
Gross Unrealized Holding Gains	0	3
Gross Unrealized Holding Losses	489	715
Fair Value	151,582	108,985
Continuous Unrealized Loss Position less than 12 Months	489	715
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | U.S. treasuries
Available-for-sale
Amortized Cost	705,370	838,825
Gross Unrealized Holding Gains	31	17
Gross Unrealized Holding Losses	2,002	4,539
Fair Value	703,399	834,303
Continuous Unrealized Loss Position less than 12 Months	2,002	4,539
Continuous Unrealized Loss Position greater than 12 Months	0	0
Short-term | Corporate bonds
Available-for-sale
Amortized Cost	158,748
Gross Unrealized Holding Gains	10
Gross Unrealized Holding Losses	462
Fair Value	158,296
Continuous Unrealized Loss Position less than 12 Months	462
Continuous Unrealized Loss Position greater than 12 Months	0
Long-term | U.S. government agency securities
Available-for-sale
Amortized Cost	2,580	2,016
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	9	3
Fair Value	2,571	2,013
Continuous Unrealized Loss Position less than 12 Months	9	3
Continuous Unrealized Loss Position greater than 12 Months	0	0
Long-term | U.S. treasuries
Available-for-sale
Amortized Cost	39,011	53,215
Gross Unrealized Holding Gains	0	20
Gross Unrealized Holding Losses	309	71
Fair Value	38,702	53,164
Continuous Unrealized Loss Position less than 12 Months	309	71
Continuous Unrealized Loss Position greater than 12 Months	0	0
Long-term | Corporate bonds
Available-for-sale
Amortized Cost	21,065
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	90
Fair Value	20,975
Continuous Unrealized Loss Position less than 12 Months	90
Continuous Unrealized Loss Position greater than 12 Months	$ 0
Long-term | Variable rate demand notes
Available-for-sale
Amortized Cost		6,266
Gross Unrealized Holding Gains		0
Gross Unrealized Holding Losses		0
Fair Value		6,266
Continuous Unrealized Loss Position less than 12 Months		0
Continuous Unrealized Loss Position greater than 12 Months		$ 0