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Capital Stock - Schedule of Share-based Compensation, Stock Options, Activity (Details) - Employee Stock Option [Member] - $ / shares
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding, beginning of period 4,892,962 5,732,209
Exercised (38,754)  
Forfeited (44,362) (14,876)
Expired (885,698) (772,665)
Cancelled (10,917) (591)
Stock options outstanding, end of period 3,913,231 4,944,077
Stock options exercisable, end of period 3,615,079 4,331,193
Stock options outstanding, weighted average exercise price per share $ 26.81 $ 26.82
Exercised, weighted average exercise price per share 21.26  
Forfeited, weighted average exercise price per share 23.12 21.78
Expired, weighted average exercise price per share 28.31 27.03
Cancelled, weighted average exercise price per share 27.20 20.85
Stock options outstanding, weighted average exercise price per share 26.56 26.80
Stock options exercisable, weighted average exercise price per share, end of period $ 26.93 $ 27.32