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Shares - Common shares (Details) - CAD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |
Beginning balance, outstanding (in shares) | 25,452,224 | 28,305,660
Issued upon exercise of stock options (in shares) | 297,940 | 176,800
Issued upon conversion of convertible debentures (in shares) | 2,211 |
Purchase of treasury shares for settlement of certain equity classified stock-based compensation (in shares) | (660,620) | (758,271)
Settlement of certain equity classified stock-based compensation (in shares) | 1,193,935 | 353,592
Retired through share purchase programs (in shares) | (1,281,485) | (2,625,557)
Ending balance, outstanding (in shares) | 25,004,205 | 25,452,224
Shares to satisfy recipient tax withholding requirements (in shares) | 553,036,000 | 161,285,000
Satisfaction of recipient tax withholding | $ 4,308 | $ 987
Common shares |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |
Beginning balance, outstanding (in shares) | 28,070,150 | 30,518,907
Issued upon exercise of stock options (in shares) | 297,940 | 176,800
Issued upon conversion of convertible debentures (in shares) | 2,211 |
Purchase of treasury shares for settlement of certain equity classified stock-based compensation (in shares) | 0 | 0
Settlement of certain equity classified stock-based compensation (in shares) | 0 | 0
Retired through share purchase programs (in shares) | (1,281,485) | (2,625,557)
Ending balance, outstanding (in shares) | 27,088,816 | 28,070,150
Treasury shares |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |
Beginning balance, outstanding (in shares) | (2,617,926) | (2,213,247)
Issued upon exercise of stock options (in shares) | 0 | 0
Issued upon conversion of convertible debentures (in shares) | 0 |
Purchase of treasury shares for settlement of certain equity classified stock-based compensation (in shares) | (660,620) | (758,271)
Settlement of certain equity classified stock-based compensation (in shares) | 1,193,935 | 353,592
Retired through share purchase programs (in shares) | 0 | 0
Ending balance, outstanding (in shares) | (2,084,611) | (2,617,926)

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- Definition Stock Issued During Period, Shares, Treasury Stock Reissued to Satisfy Shared-based Compensation Obligations + References No definition available. + Details
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- Definition The amount of adjustment to stockholders' equity associated with an employee's income tax withholding obligation as part of a net-share settlement of a share-based award. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Number of shares issued which are neither cancelled nor held in the treasury. + References No definition available. + Details
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- Definition For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer. + References No definition available. + Details
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- Definition Number of shares issued during the period as a result of the conversion of convertible securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29-30) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 + Details
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- Definition Number of share options (or share units) exercised during the current period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 + Details
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- Definition Number of shares that have been repurchased during the period and are being held in treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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