CONTRACT ASSETS AND CONTRACT LIABILITIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Accounts receivable
Accounts receivable—Members	$ 97,901	$ 105,371
Other accounts receivable	21,212	28,039
Contract liabilities
Contract liabilities (unearned revenue)	6,825	7,041
Other accounts receivable - trade
Accounts receivable
Other accounts receivable	20,519	25,355
Other accounts receivable - trade | Non-member electric sales
Accounts receivable
Other accounts receivable	3,918	4,727
Other accounts receivable - trade | Other
Accounts receivable
Other accounts receivable	16,601	20,628
Other accounts receivable, non-trade
Accounts receivable
Other accounts receivable	693	$ 2,684
Other operating revenue
Contract liabilities
Contract liabilities recognized	$ 300