AMORTIZING INTANGIBLE ASSETS - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Revenue | Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (234)	$ (389)	$ (986)	$ (1,166)
Costs And Expenses | Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,396	6,535	19,190	19,605
Costs And Expenses | Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,573	$ 1,641	$ 4,694	$ 4,818