AMORTIZING INTANGIBLE ASSETS - Recognized Amortization Expense in Other Revenues and Cost and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Revenue | Favorable gas gathering contracts
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ (389)	$ (389)
Costs And Expenses | Contract intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,397	6,535
Costs And Expenses | Rights-of-way
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,547	$ 1,585