Stock-Based Compensation (Schedule of Changes in the Number of Underlying Shares) (Details) - Restricted Stock [Member] shares in Thousands	12 Months Ended
	Apr. 30, 2016 $ / shares shares
Number of Underlying Shares [Roll Forward]
Number of shares outstanding, Beginning balance (shares) | shares	319
Number of shares outstanding, Granted (shares) | shares	55
Number of shares outstanding, Adjusted for dividends or performance (shares) | shares	(1)
Number of shares outstanding, Vested (shares) | shares	(98)
Number of shares outstanding, Forfeited (shares) | shares	(1)
Number of shares outstanding, Ending balance (shares) | shares	274
Weighted Average Fair Value at Grant Date [Roll Forward]
Weighted Average Fair Value at Grant Date, Beginning balance (dollars per share) | $ / shares	$ 72.25
Weighted Average Fair Value at Grant Date, Granted (dollars per share) | $ / shares	119.37
Weighted Average Fair Value at Grant Date, Adjusted for dividends or performance (dollars per share) | $ / shares	68.43
Weighted Average Fair Value at Grant Date, Vested (dollars per share) | $ / shares	62.59
Weighted Average Fair Value at Grant Date, Forfeited (dollars per share) | $ / shares	79.36
Weighted Average Fair Value at Grant Date, Ending balance (dollars per share) | $ / shares	$ 85.22