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Stock Option Activity (Detail)
12 Months Ended
Dec. 31, 2020
$ / shares
shares
Shares  
Outstanding at beginning of year | shares 4,766,150
Expired | shares (740,000)
Outstanding at end of year | shares 4,026,150
Exercisable at end of year | shares 4,011,150
Weighted Average Exercise Price Per Share  
Outstanding at beginning of year | $ / shares $ 20.62
Expired | $ / shares 15.10
Outstanding at end of year | $ / shares 21.63
Exercisable at end of year | $ / shares $ 21.64