REMEDIAL LIABILITIES (Additional Information) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) site	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Environmental Remediation Obligations [Abstract]
Changes in estimates recorded to statement of income (loss)	$ 11,388	$ 2,718
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
Site contingency, number of sites for remedial activities | site	4
Accrued remedial liabilities	$ 131,992	$ 155,121	$ 172,498
Possible increase in total remedial liabilities	$ 23,600
Accrual for environmental loss contingencies, threshold for disclosure (as a percent)	5.00%