INVESTMENTS - Maturity Period (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
INVESTMENTS
Amortized Cost	$ 1,482,934	$ 1,429,600
Fair Value	1,479,487	1,423,757
Commercial paper | Less than 1 year
INVESTMENTS
Amortized Cost	329,770	197,712
Fair Value	329,768	197,710
Municipal securities | Less than 1 year
INVESTMENTS
Amortized Cost	59,158	211,791
Fair Value	59,033	211,239
U.S. government agency securities | Less than 1 year
INVESTMENTS
Amortized Cost	152,071	109,697
Fair Value	151,582	108,985
U.S. government agency securities | Due 1 - 10 years
INVESTMENTS
Amortized Cost	2,580	2,016
Fair Value	2,571	2,013
Certificates of deposit | Less than 1 year
INVESTMENTS
Amortized Cost	15,161	10,078
Fair Value	15,161	10,078
U.S. treasuries | Less than 1 year
INVESTMENTS
Amortized Cost	705,370	838,825
Fair Value	703,399	834,302
U.S. treasuries | Due 1 - 10 years
INVESTMENTS
Amortized Cost	39,011	53,215
Fair Value	38,702	53,164
Corporate bonds | Less than 1 year
INVESTMENTS
Amortized Cost	158,748	0
Fair Value	158,296	0
Corporate bonds | Due 1 - 10 years
INVESTMENTS
Amortized Cost	21,065	0
Fair Value	20,975	0
Variable rate demand notes | Due 1 - 10 years
INVESTMENTS
Amortized Cost	0	4,862
Fair Value	0	4,862
Variable rate demand notes | Due 11 - 20 years
INVESTMENTS
Amortized Cost	0	1,404
Fair Value	$ 0	$ 1,404