Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Shares - Share purchase program (Details) - CAD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Aug. 14, 2017
Equity, Class of Treasury Stock [Line Items]
Shares purchased and subsequently cancelled during period (in shares)	1,281,485
2017 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Maximum number of shares to be purchased (in shares)		2,424,333
Shares purchased and subsequently cancelled during period (in shares)	1,281,485
Common shares
Equity, Class of Treasury Stock [Line Items]
Shares purchased and subsequently cancelled during period (in shares)	1,281,485
Common shares \| 2017 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Increase (decrease) as a result of the retirement of shares	$ (10,975)
Additional paid-in capital \| 2017 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Increase (decrease) as a result of the retirement of shares	$ 1,435