SHARE-BASED COMPENSATION - Summary of DSU activity (Details) - Deferred share units - shares shares in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of units, beginning of period (in shares)	5,733	4,496
Grants (in shares)	527	1,277
Exercises (in shares)	(1,168)	(40)
Number of units, end of period (in shares)	5,092	5,733

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

No definition available.

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- Definition

The number of other equity instruments (ie other than share options) granted in a share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The number of other equity instruments (ie other than share options) exercised or vested in a share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2017-01-01
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- Definition

The number of other equity instruments (ie other than share options) outstanding in a share-based payment arrangement.

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