Stock-Based Compensation (Assumptions Used To Value Options) (Details) (USD $)	12 Months Ended
	Apr. 30, 2013		Apr. 30, 2012		Apr. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term, years	3 years		3 years
Dividend yield			0.00%	[1]
Espp [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	22.32%		24.27%		22.75%
Expected volatility, maximum	27.39%		33.07%		23.31%
Expected term, years	6 months		6 months		6 months
Dividend yield, minimum	4.20%		3.68%		3.86%
Dividend yield, maximum	5.00%		4.93%		4.80%
Risk-free interest rate, minimum	0.11%		0.06%		0.19%
Risk-free interest rate, maximum	0.15%		0.10%		0.23%
Weighted-average fair value	$ 2.60		$ 2.78		$ 2.16
Stock Options For Management And Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	29.69%		31.75%		28.98%
Expected volatility, maximum	31.43%		32.34%		30.20%
Expected term, years			5 years		5 years
Dividend yield, minimum	4.18%		3.43%		4.18%
Dividend yield, maximum	5.21%		4.80%		5.17%
Risk-free interest rate, minimum	0.61%		0.79%		1.26%
Risk-free interest rate, maximum	0.75%		1.95%		1.92%
Weighted-average fair value	$ 2.79		$ 3.31		$ 2.25
Performance Nonvested Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	12.61%		20.68%
Expected volatility, maximum	71.96%		143.12%
Dividend yield, minimum	0.00%	[1]
Dividend yield, maximum	5.01%	[1]
Risk-free interest rate	0.40%		0.75%
Weighted-average fair value	$ 16.72		$ 17.46
Minimum [Member] | Stock Options For Management And Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term, years	4 years
Maximum [Member] | Stock Options For Management And Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term, years	5 years

[1] The valuation model assumes that dividends are reinvested by the issuing entity on a continuous basis.