Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Earnings Per Share [Abstract]
Net income from continuing operations attributable to shareholders	$ 688,922	$ (16,915)	$ (101,199)	$ (105,650)	$ 591,703	$ (3,567)	$ (123,013)	$ (119,155)	$ 465,158	$ 345,968	$ 392,547
Net income allocated to participating securities									(542)	(455)	(1,007)
Net income from continuing operations attributable to common shareholders									$ 464,616	$ 345,513	$ 391,540
Basic weighted average common shares (in shares)									273,057,000	297,863,000	309,230,000
Potential dilutive shares									1,302,000	738,000	547,000
Dilutive weighted average common shares									274,359,000	298,601,000	309,777,000
Basic (in usd per share)	$ 2.53	$ (0.06)	$ (0.37)	$ (0.38)	$ 2.02	$ (0.01)	$ (0.41)	$ (0.39)	$ 1.70	$ 1.16	$ 1.27
Diluted (in usd per share)	$ 2.51	$ (0.06)	$ (0.37)	$ (0.38)	$ 2.01	$ (0.01)	$ (0.41)	$ (0.39)	$ 1.69	$ 1.16	$ 1.27
Antidilutive securities excluded from computation of earnings per share, amount									3,300,000	8,900,000	12,800,000