Stock-Based Compensation Other (Details)	12 Months Ended
	Apr. 30, 2017 $ / shares shares
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	$ 0.59
Range of Exercise Price, high end of range (in dollars per share)	$ 32.19
Options Outstanding
Number of Options (in shares) | shares	517,264
Weighted Average Remaining Contractual Life In Years	5 years 1 month 17 days
Weighted Average Exercise Price (in dollars per share)	$ 21.83
Options Exercisable
Number of Options Exercisable (in shares) | shares	377,146
Weighted Average Exercise Price (in dollars per share)	$ 20.36
Weighted Average Remaining Contractual Life	4 years 3 months 29 days
0.59 - 18.32
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	$ 0.59
Range of Exercise Price, high end of range (in dollars per share)	$ 18.32
Options Outstanding
Number of Options (in shares) | shares	115,640
Weighted Average Remaining Contractual Life In Years	4 years 3 months
Weighted Average Exercise Price (in dollars per share)	$ 8.15
Options Exercisable
Number of Options Exercisable (in shares) | shares	108,040
Weighted Average Exercise Price (in dollars per share)	$ 7.45
18.33 - 22.90
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	18.33
Range of Exercise Price, high end of range (in dollars per share)	$ 22.90
Options Outstanding
Number of Options (in shares) | shares	98,000
Weighted Average Remaining Contractual Life In Years	4 years 6 months 22 days
Weighted Average Exercise Price (in dollars per share)	$ 19.87
Options Exercisable
Number of Options Exercisable (in shares) | shares	74,000
Weighted Average Exercise Price (in dollars per share)	$ 19.97
22.91 - 26.99
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	22.91
Range of Exercise Price, high end of range (in dollars per share)	$ 26.99
Options Outstanding
Number of Options (in shares) | shares	134,600
Weighted Average Remaining Contractual Life In Years	5 years 7 months 28 days
Weighted Average Exercise Price (in dollars per share)	$ 25.77
Options Exercisable
Number of Options Exercisable (in shares) | shares	68,600
Weighted Average Exercise Price (in dollars per share)	$ 24.91
27.00 - 29.26
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	27.00
Range of Exercise Price, high end of range (in dollars per share)	$ 29.26
Options Outstanding
Number of Options (in shares) | shares	100,000
Weighted Average Remaining Contractual Life In Years	5 years 8 months 12 days
Weighted Average Exercise Price (in dollars per share)	$ 28.00
Options Exercisable
Number of Options Exercisable (in shares) | shares	80,000
Weighted Average Exercise Price (in dollars per share)	$ 28.18
29.27 - 32.19
Stock-Based Compensation
Range of Exercise Price, low end of range (in dollars per share)	29.27
Range of Exercise Price, high end of range (in dollars per share)	$ 32.19
Options Outstanding
Number of Options (in shares) | shares	69,024
Weighted Average Remaining Contractual Life In Years	5 years 6 months 15 days
Weighted Average Exercise Price (in dollars per share)	$ 30.94
Options Exercisable
Number of Options Exercisable (in shares) | shares	46,506
Weighted Average Exercise Price (in dollars per share)	$ 30.78