Stock-based Payments - Stock Purchase Warrants Activity (Details) - Warrant - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Shares, Beginning Balance	2,004,284	2,109,840
Number of Shares, Granted	0	0
Number of Shares, Exercised	0	0
Number of Shares, Forfeited	0	0
Number of Shares, Expired	0	(105,556)
Number of Shares, Ending Balance	2,004,284	2,004,284	2,109,840
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Exercise Price, Beginning Balance (in usd per share)	$ 5.57	$ 5.54
Weighted Average Exercise Price, Granted (in usd per share)	0.00	0.00
Weighted Average Exercise Price, Exercised (in usd per share)	0.00	0.00
Weighted Average Exercise Price, Forfeited (in usd per share)	0.00	0.00
Weighted Average Exercise Price, Expired (in usd per share)	0.00	4.80
Weighted Average Exercise Price, Ending Balance (in usd per share)	$ 5.57	$ 5.57	$ 5.54
Weighted Average Remaining Contractual Life (Years), Balance	1 year 9 months 18 days	2 years 9 months 18 days	3 years 7 months 6 days
Weighted Average Remaining Contractual Life (Years), Granted	0 years
Aggregate Intrinsic Value, Beginning Balance	$ 0	$ 0
Aggregate Intrinsic Value, Granted	0	0
Aggregate Intrinsic Value, Ending Balance	$ 0	$ 0	$ 0