Loss Per Share and Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Antidilutive securities excluded from computation of earnings per share, amount (in shares)			4,500	4,600
Net loss from continuing operations attributable to shareholders	$ (101,212)	$ (78,649)	$ (365,653)	$ (317,672)
Amounts allocated to participating securities	(143)	(112)	(410)	(316)
Net loss from continuing operations attributable to common shareholders	$ (101,355)	$ (78,761)	$ (366,063)	$ (317,988)
Basic weighted average common shares (in shares)	207,862	231,904	214,627	257,979
Potential dilutive shares (in shares)	0	0	0	0
Weighted Average Number of Shares Outstanding, Diluted	207,862	231,904	214,627	257,979
Basic (in usd per share)	$ (0.49)	$ (0.34)	$ (1.71)	$ (1.23)
Narrative Details [Abstract]
Stock Repurchased and Retired During Period, Shares			14,000	52,500
Stock Repurchased and Retired During Period, Value			$ 317,020	$ 1,891,838
Accelerated Share Repurchases, Final Price Paid Per Share			$ 22.61	$ 36.02
Shares repurchased during the period, (in shares)			300	600
Shares repurchased during the period, Value			$ 5,800	$ 17,900
Shares issued during period (in shares)			900	2,200
Nonvested units granted			1,200
Stock-based compensation	$ 4,500	$ 7,200	$ 16,900	$ 21,100
Unrecognized compensation costs, options	100		100
Unrecognized compensation costs, nonvested shares and units	$ 33,500		33,500
Common Stock [Member]
Narrative Details [Abstract]
Stock Repurchased and Retired During Period, Value			140	525
Additional Paid-in Capital [Member]
Narrative Details [Abstract]
Stock Repurchased and Retired During Period, Value			8,412	31,506
Retained Earnings [Member]
Narrative Details [Abstract]
Stock Repurchased and Retired During Period, Value			$ 308,468	$ 1,859,807