Stock-Based Compensation Non-Vested Stock Options (Details) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Options
Options granted (in shares)	0
Weighted Average Grant Date Fair value
Unrecognized compensation cost related to non-vested stock awards	$ 8,248,000
Period over which unrecognized compensation cost is expected to be recognized	3 years
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 4 months 24 days
Tax benefit realized from stock-based compensation	$ 0	$ 98,000	$ 191,000
Stock options
Options
Non-vested at beginning of year (in shares)	292,513
Canceled (in shares)	(60,619)
Vested (in shares)	(91,776)
Non-vested at end of year (in shares)	140,118	292,513
Weighted Average Grant Date Fair value
Non-vested at beginning of year (in dollars per share)	$ 10.53
Granted (in dollars per share)		$ 10.18	$ 14.05
Canceled (in dollars per share)	10.71
Vested (in dollars per share)	10.07
Non-vested at end of year (in dollars per share)	$ 10.76	$ 10.53
Fair value of shares vested	$ 3,332,000	$ 2,965,000	$ 2,389,000
Proceeds from exercises of options	$ 3,865,000	$ 1,122,000	$ 722,000