Significant Accounting Policies - Calculation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Basic loss per share computation
Net income (loss) attributable to common stockholders	$ 307	$ (641)	$ 267	$ 483	$ (334)	$ 750
Weighted Average common shares - basic (in shares)	11,619,686		11,278,312		11,619,569	11,135,358
Basic net income (loss) per share (in dollars per share)	$ 0.03		$ 0.02		$ (0.03)	$ 0.07
Income (loss) available to common stockholders	$ 307		$ 267		$ (334)	$ 750
Incremental shares from assumed exercise of warrants and stock options (in shares)	1,345,106		2,758,778		0	2,356,144
Adjusted weighted average share - diluted (in shares)	12,964,792		14,037,090		11,619,569	13,491,502
Diluted net income (loss) per share (in usd per share)	$ 0.02		$ 0.02		$ (0.03)	$ 0.06