Stock-Based Compensation Non-Vested Stock Options (Details) - USD ($)	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Options
Options granted (in shares)	0	0
Weighted Average Grant Date Fair value
Unrecognized compensation cost related to non-vested stock awards	$ 7,045,000
Period over which unrecognized compensation cost is expected to be recognized	2 years
Weighted average period over which unrecognized compensation cost is expected to be recognized	1 year 10 months 24 days
Exercise of stock options	$ 2,705,000	$ 3,865,000	$ 1,122,000
Excess tax benefit from stock-based compensation	$ 0	$ 0	$ 98,000
Stock options
Options
Non-vested at beginning of year (in shares)	140,118
Vested (in shares)	(57,104)
Non-vested at end of year (in shares)	83,014	140,118
Weighted Average Grant Date Fair value
Non-vested at beginning of year (in dollars per share)	$ 10.76
Granted (in dollars per share)			$ 10.18
Vested (in dollars per share)	10.45
Non-vested at end of year (in dollars per share)	$ 10.97	$ 10.76
Exercise of stock options	$ 2,576,000	$ 3,863,000	$ 1,121,000
Fair value of shares vested	$ 3,328,000	$ 2,942,000	$ 2,495,000