INVESTMENTS - Maturity Period (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
INVESTMENTS
Amortized Cost	$ 1,429,600	$ 1,850,101
Fair Value	1,423,757	1,849,146
Commercial paper | Less than 1 year
INVESTMENTS
Amortized Cost	197,712	334,077
Fair Value	197,710	334,077
Municipal securities | Less than 1 year
INVESTMENTS
Amortized Cost	211,791	666
Fair Value	211,239	666
U.S. government agency securities | Less than 1 year
INVESTMENTS
Amortized Cost	109,697	62,687
Fair Value	108,985	62,661
U.S. government agency securities | Due 1 - 10 years
INVESTMENTS
Amortized Cost	2,016	12,500
Fair Value	2,013	12,476
Certificates of deposit | Less than 1 year
INVESTMENTS
Amortized Cost	10,078	44,502
Fair Value	10,078	44,502
U.S. treasuries | Less than 1 year
INVESTMENTS
Amortized Cost	838,825	1,308,536
Fair Value	834,302	1,307,821
U.S. treasuries | Due 1 - 10 years
INVESTMENTS
Amortized Cost	53,215	87,133
Fair Value	53,164	$ 86,943
Variable rate demand notes | Due 1 - 10 years
INVESTMENTS
Amortized Cost	4,862
Fair Value	4,862
Variable rate demand notes | Due 11 - 20 years
INVESTMENTS
Amortized Cost	1,404
Fair Value	$ 1,404