Other Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019		Apr. 30, 2018
Fair Value Disclosures [Abstract]
Company's Municipal bond mature in 2021	$ 1.0
Company's Municipal bond mature in 2022	1.5
Company's Municipal bond mature in 2023	0.0
Company's Municipal bond mature in 2024	3.5
Company's Municipal bond mature in 2025 and beyond	18.2
Impairment charges	52.4	$ 205.1
Goodwill impairment charges	0.0	97.9	[1]	$ 145.0
Other intangible assets impairment charges	$ 52.4	$ 107.2		$ 31.9

[1] We have recognized accumulated goodwill impairment charges of $242.9 as of April 30, 2020.