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Capital Stock - Summary of Stock Option Activity and Related Information (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Options      
Options Outstanding - beginning of year (shares) 6,066,000 3,754,000 3,600,000
Options, Granted (in shares) 0 2,620,000 1,052,000
Options, Exercised (shares) 0 0 (2,000)
Options, Forfeited / expired (shares) (491,000) (308,000) (896,000)
Options Outstanding - end of year (shares) 5,575,000 6,066,000 3,754,000
Options Exercisable - end of year (shares) 3,490,000 2,565,000 1,954,000
Weighted-Average Exercise Price      
Weighted-Average Exercise Price, Outstanding - beginning of year (dollars per share) $ 10.77 $ 15.54 $ 22.96
Weighted-Average Exercise Price, Granted (dollars per share) 0 3.98 8.67
Weighted-Average Exercise Price, Exercised (dollars per share) 0 0 9.44
Weighted-Average Exercise Price, Forfeited / expired (dollars per share) 19.35 11.07 37.44
Weighted-Average Exercise Price, Outstanding - end of year (dollars per share) 10.02 10.77 15.54
Weighted-Average Exercise Price, Exercisable - end of year (dollars per share) $ 13.17 $ 18.25 $ 21.35
Stock Options      
Options      
Options, Granted (in shares) 0 2,620,582 1,048,916