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Goodwill and Intangible Assets - Summary of Change in Net Carrying Value of Goodwill (Detail) - USD ($)
$ in Millions
6 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Goodwill And Intangible Assets Disclosure [Abstract]    
Balance at beginning of period $ 161.8 $ 133.2
Activity from prior year acquisitions (2.0) 2.4
Activity from current year acquisitions   51.4
Balance at end of period $ 159.8 $ 187.0