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Deferred Compensation - Additional Information (Detail) - USD ($)
$ in Millions
Jan. 31, 2018
Jan. 31, 2017
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]    
Marketable securities $ 436.0  
Rabbi Trust    
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]    
Deferred compensation liability current 3.4 $ 3.1
Deferred compensation liability non-current 55.6 44.2
Marketable Securities, Current    
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]    
Trading securities 59.0 47.3
Marketable Securities, Current | Rabbi Trust    
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]    
Trading securities $ 59.0 $ 47.3