INCOME TAXES - Reconciliation of Statutory Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Statutory income tax	$ 22,065	$ 22,858	$ 16,965
Increase (reduction) in taxes due to:
State income taxes net of federal tax benefit	7,334	7,598	5,639
Effect of regulatory treatment of fixed asset differences	(6,327)	(9,201)	(3,696)
Investment tax credits	(74)	(74)	(74)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	(891)	(1,392)	(1,870)
Stock based stock compensation	791	523	302
TCJA refund	(19,417)	(9,470)	0
Other	611	1,176	405
Total income tax	$ 4,092	$ 12,018	$ 17,671