REVENUE (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Unbilled Receivables, Current	$ 52,000,000.0		$ 52,000,000.0		$ 109,700,000
Regulated Operating Revenue, Gas	240,828,000	$ 244,380,000	1,030,682,000	$ 1,194,307,000
Regulated Operating Revenue, Other	3,812,000	4,183,000	15,413,000	5,816,000
Regulated Operating Revenue	244,640,000	248,563,000	1,046,095,000	1,200,123,000
Natural gas sales to customers [Member]
Regulated Operating Revenue, Gas	212,723,000	215,996,000	936,749,000	1,096,048,000
Transportation revenues [Member]
Regulated Operating Revenue, Gas	24,305,000	23,707,000	82,543,000	82,726,000
Miscellaneous revenues [Member]
Regulated Operating Revenue, Gas	3,800,000	4,677,000	11,390,000	15,533,000
Other revenues - natural gas sales related [Member]
Other revenues - natural gas sales related	(66,000)	735,000	6,478,000	(2,002,000)
Other revenues [Member]
Regulated Operating Revenue, Other	$ 3,878,000	$ 3,448,000	$ 8,935,000	$ 7,818,000