Loss Per Share and Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	3,400	3,300	3,400	3,300
Basic weighted average common shares (in shares)	205,532	209,080	206,242	208,693
Shares retired during period (in shares)			4,700
Shares retired during year, value				$ 109,406
Shares retired during the year, average price (in usd per share)			$ 23.29
Shares repurchased during the period, (in shares)			200	300
Shares repurchased during the period, value			$ 5,000	$ 7,700
Shares issued during period (in shares)			700	2,200
Nonvested units granted			1,000
Stock-based compensation	$ 6,200	$ 5,400	$ 18,000	$ 17,100
Unrecognized compensation costs, options	700		700
Unrecognized compensation costs, nonvested shares and units	$ 31,800		$ 31,800