COMMITMENTS AND CONTINGENCIES - Part 2 (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2016	Dec. 31, 2017 USD ($)	Jan. 01, 2017 USD ($)
Commitments and Contingencies [Line Items]
Number Of Former Manufactured Gas Sites Where We Own Or Retain Legal Responsibility For Environmental Conditions	12
Number of MGP sites for which a remediation reserve was recorded	1
Deferred MGP Costs, Maximum			$ 15,000
Regulatory assets	$ 437,479		$ 405,189
Number of sites with ongoing groundwater monitoring	8
Environmental Reserve Estimate Range, Low	5.6	4
Environmental Reserve Estimate Range, High	7.0	7
Accrual for Environmental Loss Contingencies, Revision in Estimates	$ 1,600
Environmental Reserve Estimate, Actual	5.6
Percentage yield of high consequence pipeline areas			30.00%
MGP Costs [Member]
Commitments and Contingencies [Line Items]
Regulatory assets	$ 7,724		$ 6,104	$ 5,900