Business, Basis of Presentation and Summary of Significant Accounting Policies - Restructuring charges (Details) $ in Millions	3 Months Ended	12 Months Ended
Apr. 30, 2020 USD ($) facility	Apr. 30, 2020 USD ($)	Apr. 30, 2019 USD ($)
Restructuring costs	$ 2.2
Number of facilities closed \| facility	1
Impairment	$ 1.9	$ 1.9
Severance	$ 0.3
Selling, general and administrative expenses
Restructuring costs			$ 5.0

Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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