Loss Per Share and Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	3,400	3,400	3,400	3,400
Basic weighted average common shares (in shares)	205,520	209,065	206,596	208,500
Shares retired during period (in shares)	4,200
Shares retired during year, value				$ 97,105
Shares retired during the year, average price (in usd per share)	$ 23.27
Shares repurchased during the period, (in shares)			200	200
Shares repurchased during the period, value			$ 5,000	$ 7,600
Shares issued during period (in shares)			700	2,100
Nonvested units granted			1,000
Stock-based compensation	$ 7,500	$ 6,800	$ 11,800	$ 11,600
Unrecognized compensation costs, options	900		900
Unrecognized compensation costs, nonvested shares and units	$ 37,900		$ 37,900