CONTINGENCIES AND COMMITMENTS (Regulatory Proceedings) (Details) - USD ($) $ in Thousands			6 Months Ended
	May 17, 2018	Apr. 26, 2018	Jun. 30, 2018
Ex Parte Communications
Loss Contingencies [Line Items]
Proposed penalty		$ 97,500
Payment to State General Fund	$ 12,000	12,000
Gas transmission and storage revenue reduction		63,500
2018 GTandS revenue requirement reduction		31,750
2019 GTandS revenue requirement reduction		31,750
Revenue requirement reduction in Next GRC cycle		10,000
Payment to city of San Bruno	6,000	6,000
Payment to city of San Carlos	$ 6,000	$ 6,000
Disallowance of Plant Costs
Loss Contingencies [Line Items]
Accrual for GTandS revenue requirement reduction			$ 16,000