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Stock-Based Compensation Plans - Narrative (Detail)
3 Months Ended
Mar. 31, 2018
$ / shares
Stock Options  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Grant date fair value (in USD per share) $ 17.37
Performance Unit Awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted (in USD per share) $ 0.83