Share-Based Payments - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 148,000	$ 535,000	$ 711,000	$ 1,664,000
Option modification charge			56,529
Unrecognized compensation cost	$ 160,365		$ 160,365
Period for recognition			2 years 6 months
Weighted-average grant date fair value (in usd per share)	$ 0.00	$ 1.16	$ 1.84	$ 1.73
Shares granted (in shares)			194,977
Grants in period, weighted average exercise price (in usd per share)			$ 2.51
Warrants outstanding (in shares)	2,004,284		2,004,284