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Stock-based Compensation Plans - Stock Option and SARs Activities (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Exercised, Shares 0 0 (77,002)
Stock Appreciation Rights (SARs)      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Beginning Balance, Shares 1,003,600 1,510,977 1,966,549
Exercised, Shares     (427,598)
Expired/forfeited, Shares (620,821) (507,377) (27,974)
Ending Balance, Shares 382,779 1,003,600 1,510,977
Beginning Balance, Weighted Average Exercise Price $ 69.08 $ 63.73 $ 59.80
Exercised, Weighted Average Exercise Price     45.67
Expired/forfeited, Weighted Average Exercise Price 62.29 53.16 63.10
Ending Balance, Weighted Average Exercise Price $ 76.54 $ 69.08 $ 63.73