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Capital Stock - Additional Information (Details) | 1 Months Ended | 2 Months Ended | 3 Months Ended | 11 Months Ended | 12 Months Ended | 13 Months Ended |  |  |
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Dec. 31, 2018 USD ($) shares vote / shares | Dec. 31, 2017 USD ($) shares $ / shares | May 31, 2016 USD ($) $ / shares shares | Nov. 30, 2018 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) shares $ / shares | Dec. 31, 2018 USD ($) shares vote / shares | Dec. 31, 2018 USD ($) shares vote / shares | Dec. 31, 2018 USD ($) shares vote / shares | Dec. 31, 2018 USD ($) shares vote / shares | Dec. 31, 2017 USD ($) shares director $ / shares | Dec. 31, 2016 USD ($) shares $ / shares | Nov. 30, 2018 $ / shares shares | Feb. 28, 2017 shares | Nov. 30, 2017 shares | Feb. 29, 2016 shares | Dec. 31, 2015 shares
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment to repurchase and cancel shares | $ |  |  |  |  |  |  |  |  | $ 75,500,000 | $ 19,900,000 | [1] | $ 34,300,000 | [1] |  |  |  |  |
Employee stock-based compensation expense | $ |  |  |  |  |  |  |  |  | 33,400,000 | $ 30,100,000 |  | $ 33,000,000 |  |  |  |  |  |
Number of share options granted in share-based payment arrangement |  |  |  |  |  |  | 0 |  |  | 0 |  | 0 |  |  |  |  |  |
Weighted average share price for share options in share-based payment arrangement exercised during period at date of exercise | $ |  |  |  |  |  |  |  |  | 10.92 | $ 12.41 |  | $ 10.66 |  |  |  |  |  |
Value of shares purchased | $ |  |  |  |  |  |  |  |  | $ 22,400,000 | $ 16,700,000 |  | $ 18,200,000 |  |  |  |  |  |
Number of resigned directors | director |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |
Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expiration period |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 4 years |  |  |  |  |  |  |  |  |  |  |  |
PSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares vested dependent on performance achievements |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 1,600,000 |  |  | 900,000 |  | 1,250,000 |  |  |  |  |  |
Percentage of shares that will vest based on market performance condition and total shareholder return |  |  |  |  |  |  |  |  |  | 60.00% |  | 60.00% |  |  |  |  |  |
Award requisite service period |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |
Premium used in estimating grant date fair value |  |  |  |  |  |  |  | 106.00% |  | 143.00% |  | 109.00% |  |  |  |  |  |
Number of other equity instruments exercised or vested in share-based payment arrangement (in shares) |  |  |  |  |  |  | 400,000 | 0 |  | 800,000 |  | 1,100,000 |  |  |  |  |  |
Number of shares outstanding (in shares) | 3,200,000 | 2,500,000 |  |  | 3,000,000 | 3,200,000 | 3,200,000 | 3,200,000 | 3,200,000 | 2,500,000 |  | 3,000,000 |  |  |  |  |  |
Weighted average grant date fair value (in dollars per share) | $ | $ 11.11 | $ 17.18 |  |  | $ 9.61 | $ 11.11 | $ 11.11 | $ 11.11 | $ 11.11 | $ 17.18 |  | $ 9.61 |  |  |  |  |  |
RSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 2,600,000 |  |  | 1,900,000 |  | 2,300,000 |  |  |  |  |  |
Number of other equity instruments exercised or vested in share-based payment arrangement (in shares) |  |  |  |  |  |  | 1,800,000 | 0 |  | 2,300,000 |  | 1,900,000 |  |  |  |  |  |
Number of shares outstanding (in shares) | 3,800,000 | 3,200,000 |  |  | 3,800,000 | 3,800,000 | 3,800,000 | 3,800,000 | 3,800,000 | 3,200,000 |  | 3,800,000 |  |  |  |  |  | 3,500,000
Weighted average grant date fair value (in dollars per share) | $ | $ 10.48 | $ 13.05 |  |  | $ 9.29 | $ 10.48 | $ 10.48 | $ 10.48 | $ 10.48 | $ 13.05 |  | $ 9.29 |  |  |  |  |  |
DSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock-based compensation expense | $ |  |  |  |  |  |  |  |  | $ 2,000,000 | $ 2,200,000 |  | $ 2,100,000 |  |  |  |  |  |
Number of other equity instruments exercised or vested in share-based payment arrangement (in shares) |  |  |  |  |  |  |  |  |  | 14,098 |  |  |  |  |  |  |  |
Number of shares outstanding (in shares) | 1,600,000 | 1,500,000 |  |  | 1,300,000 | 1,600,000 | 1,600,000 | 1,600,000 | 1,600,000 | 1,500,000 |  | 1,300,000 |  |  |  |  |  |
Payments to settle DSUs as a result of a director's resignation | $ |  |  |  |  |  |  |  |  |  | $ 1,700,000 |  |  |  |  |  |  |  |
LTIP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 700,000 |  |  |  |  |  |  |  |  |  |  |
LTIP | RSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 0 |  |  | 1,400,000 |  | 800,000 |  |  |  |  |  |
Number of other equity instruments exercised or vested in share-based payment arrangement (in shares) |  |  |  |  |  |  | 900,000 |  |  | 300,000 |  | 0 |  |  |  |  |  |
Number of shares outstanding (in shares) | 700,000 | 1,700,000 |  |  | 800,000 | 700,000 | 700,000 | 700,000 | 700,000 | 1,700,000 |  | 800,000 |  |  |  |  |  | 0
CSUP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 2,500,000 |  |  |  |  |  |  |  |  |  |  |
CSUP | RSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares granted (in shares) |  |  |  |  |  |  | 2,600,000 |  |  | 500,000 |  | 1,500,000 |  |  |  |  |  |
Number of other equity instruments exercised or vested in share-based payment arrangement (in shares) |  |  |  |  |  |  | 900,000 |  |  | 2,000,000 |  | 1,900,000 |  |  |  |  |  |
Number of shares outstanding (in shares) | 3,100,000 | 1,500,000 |  |  | 3,000,000 | 3,100,000 | 3,100,000 | 3,100,000 | 3,100,000 | 1,500,000 |  | 3,000,000 |  |  |  |  |  | 3,500,000
Bottom of range | PSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares vested dependent on performance achievements |  |  |  |  |  |  |  | 0.00% |  |  |  |  |  |  |  |  |  |
Top of range | PSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares vested dependent on performance achievements |  |  |  |  |  |  |  | 200.00% |  |  |  |  |  |  |  |  |  |
Subordinate voting shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subordinate voting shares, number of votes per share | vote / shares | 1 |  |  |  |  | 1 | 1 | 1 | 1 |  |  |  |  |  |  |  |  |
Number of shares issued | 117,700,000 | 123,200,000 |  |  | 121,900,000 | 117,700,000 | 117,700,000 | 117,700,000 | 117,700,000 | 123,200,000 |  | 121,900,000 |  |  |  |  |  | 124,500,000
Number of shares repurchased and cancelled (in shares) |  |  |  |  |  |  | 6,800,000 |  |  | 1,900,000 |  | 3,200,000 |  |  |  |  |  |
Number of shares purchased |  |  |  |  |  |  | 2,100,000 |  |  | 1,400,000 |  | 1,600,000 |  |  |  |  |  |
Value of shares purchased | $ |  |  |  |  |  |  |  |  | $ 22,400,000 | $ 16,700,000 |  | $ 18,200,000 |  |  |  |  |  |
Number of shares acquired and held by broker | 1,900,000 | 800,000 |  |  | 1,400,000 | 1,900,000 | 1,900,000 | 1,900,000 | 1,900,000 | 800,000 |  | 1,400,000 |  |  |  |  |  |
Value of shares acquired and held by broker | $ | $ 20,200,000 | $ 8,700,000 |  |  | $ 15,300,000 | $ 20,200,000 | $ 20,200,000 | $ 20,200,000 | $ 20,200,000 | $ 8,700,000 |  | $ 15,300,000 |  |  |  |  |  |
Subordinate voting shares | LTIP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized |  |  |  |  |  |  | 29,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Shares remaining in reserve for issuance | 11,100,000 |  |  |  |  | 11,100,000 | 11,100,000 | 11,100,000 | 11,100,000 |  |  |  |  |  |  |  |  |
Subordinate voting shares | 2018 NCIB |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased | 9,500,000 |  |  |  |  | 9,500,000 | 9,500,000 | 9,500,000 | 9,500,000 |  |  |  |  |  |  |  |  |
Shares repurchased (in shares) | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subordinate voting shares | 2017 NCIB |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,500,000 |  |
Payment to repurchase and cancel shares | $ |  | $ 19,900,000 |  | $ 75,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares repurchased and cancelled (in shares) |  | 1,900,000 |  | 6,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares repurchased (in shares) |  | 300,000 |  |  |  |  |  |  |  |  |  |  |  | 1,100,000 |  |  |  |
Subordinate voting shares | 2017 NCIB | Weighted average |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) | $ / shares |  | $ 10.58 |  | $ 11.10 |  |  |  |  |  | $ 10.58 |  |  |  | $ 11.10 |  |  |  |
Subordinate voting shares | 2016 NCIB |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,500,000 |
Payment to repurchase and cancel shares | $ |  |  |  |  | $ 34,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares repurchased and cancelled (in shares) |  |  |  |  | 3,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Shares repurchased (in shares) |  |  |  |  |  |  |  |  |  | 0 |  | 1,600,000 |  |  | 1,600,000 |  |  |
Subordinate voting shares | 2016 NCIB | Weighted average |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) | $ / shares |  |  |  |  | $ 10.69 |  |  |  |  |  |  | $ 10.69 |  |  |  |  |  |
Subordinate voting shares | Program Share Repurchase, 2016 NCIB |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares repurchased and cancelled (in shares) |  |  | 2,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized amount to be repurchased | $ |  |  | $ 30,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subordinate voting shares | Program Share Repurchase, 2016 NCIB | Weighted average |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) | $ / shares |  |  | $ 10.69 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Multiple voting shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subordinate voting shares, number of votes per share | vote / shares | 25 |  |  |  |  | 25 | 25 | 25 | 25 |  |  |  |  |  |  |  |  |
Number of shares issued | 18,600,000 | 18,600,000 |  |  | 18,900,000 | 18,600,000 | 18,600,000 | 18,600,000 | 18,600,000 | 18,600,000 |  | 18,900,000 |  |  |  |  |  | 18,900,000
Number of shares repurchased and cancelled (in shares) |  |  |  |  |  |  | 0 |  |  | 0 |  | 0 |  |  |  |  |  |
Preferred shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares issued | 0 |  |  |  |  | 0 | 0 | 0 | 0 |  |  |  |  |  |  |  |  |
[1] | Certain prior period figures have been restated to reflect the adoption of IFRS 15 (see note 2)

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