REMEDIAL LIABILITIES (Additional Information) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) site	Dec. 31, 2014 USD ($)
Environmental Remediation Obligations [Abstract]
Changes in estimates recorded to statement of income (loss)	$ (1,635)	$ (11,388)
Site contingency, number of sites for remedial activities | site		4
Changes in remediation liabilities due to change in estimates of amounts recoverable from a third party		$ 3,800
Changes in remediation liabilities due to revisions from third party consultants		4,700
Changes in remediation liabilities due to provincial approval for planned expansion		2,500
Future remediation liability	128,007	$ 131,992	$ 155,121
Possible increase in total remedial liabilities	$ 23,400
Accrual for environmental loss contingencies, threshold for disclosure (as a percent)	5.00%