NON-CONTROLLING INTEREST - Narrative (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Eagle Rock Materials Ltd.
Noncontrolling Interest [Line Items]
Interest held by the company (percent)	70.00%
Orca
Noncontrolling Interest [Line Items]
Interest held by the company (percent)	88.00%
Namgis First Nation \| Orca
Noncontrolling Interest [Line Items]
Ownership percentage, by non-controlling interest holders (percent)	12.00%
Polaris \| Namgis First Nation
Noncontrolling Interest [Line Items]
Loans to related party		$ 8.0
Loan annual interest rate (percent)	6.00%
Percentage of entitled amount to be paid in cash (percent)	50.00%

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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