Loss Per Share and Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Earnings Per Share [Abstract]
Net loss from continuing operations attributable to shareholders	$ (242,925)	$ (101,212)	$ (519,055)	$ (365,653)
Amounts allocated to participating securities	(177)	(143)	(498)	(410)
Net loss from continuing operations attributable to common shareholders	$ (243,102)	$ (101,355)	$ (519,553)	$ (366,063)
Basic weighted average common shares (in shares)	209,080	207,862	208,693	214,627
Potential dilutive shares (in shares)	0	0	0	0
Dilutive weighted average common shares (in shares)	209,080	207,862	208,693	214,627
Basic (in usd per share)	$ (1.16)	$ (0.49)	$ (2.49)	$ (1.71)
Narrative Details [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)			3,300	4,500
Shares retired during period (in shares)				14,000
Shares retired during year, value				$ 317,000
Shares retired during the year, average price (in usd per share)				$ 22.61
Shares repurchased during the period, (in shares)			300	300
Shares repurchased during the period, value			$ 7,700	$ 5,800
Shares issued during period (in shares)			2,200	900
Nonvested units granted			1,200
Stock-based compensation	$ 5,400	$ 4,500	$ 17,100	$ 16,900
Unrecognized compensation costs, options	1,200		1,200
Unrecognized compensation costs, nonvested shares and units	$ 35,700		$ 35,700