Share-Based Payments - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018	Apr. 30, 2019
Share-based Payment Arrangement [Abstract]
Stock-based compensation expense	$ 77,000	$ 88,000	$ 208,000	$ 171,000
Option modification charge (reduction)				$ 7,500
Unvested options forfeited (in shares)			40,000
Unvested options, negative expense			$ (37,000)
Weighted-average grant date fair value (in usd per share)	$ 3.32	$ 6.17	$ 3.32	$ 6.16
Warrants outstanding (in shares)	1,669,773		1,669,773		1,671,440