COMMITMENTS AND CONTINGENCIES (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Accrual for estimated environmental remediation costs	$ 9,083	$ 10,010	$ 9,083		$ 10,010	$ 9,083	$ 4,979	$ 12,770
Environmental liability, next 12 month		1,100			1,100
Environmental liability thereafter		8,900			8,900
Environmental remediation		1,600	2,700	$ 2,900	1,576	5,600	0
Additions to accrual	2,700	1,600		$ 2,900	1,576	5,600	$ 0
Performance bonds outstanding	$ 7,500	$ 4,200	$ 7,500		$ 4,200	$ 7,500
Minimum
Site Contingency [Line Items]
Remediation period					2 years
Remediation activity monitoring period					10 years
Maximum
Site Contingency [Line Items]
Remediation period					3 years
Remediation activity monitoring period					15 years