Loss Per Share and Stockholders' Equity (Narrative) (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended	6 Months Ended
Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	3,700	3,400	3,700	3,400
Basic weighted average common shares (in shares)	198,079	205,520	200,058	206,596
Shares repurchased during the period, (in shares)			300	200
Shares repurchased during the period, value			$ 9.4	$ 5.0
Shares issued during period (in shares)	900	700
Nonvested units granted			1,400
Stock-based compensation	$ 9.4	$ 7.5	$ 16.1	$ 11.8
Unrecognized compensation costs, options	0.4		0.4
Unrecognized compensation costs, nonvested shares and units	$ 47.1		$ 47.1

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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