Significant Accounting Policies - Calculation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Basic loss per share computation
Net income (loss) attributable to common stockholders	$ 407	$ 307	$ (641)	$ (369)	$ 267	$ 483	$ 72	$ 381
Weighted Average common shares - basic (in shares)	11,752,619			11,508,180			11,653,115	11,257,314
Basic net income (loss) per share (in dollars per share)	$ 0.03			$ (0.03)			$ 0.01	$ 0.03
Income (loss) available to common stockholders	$ 407			$ (369)			$ 72	$ 381
Incremental shares from assumed exercise of warrants and stock options (in shares)	1,921,053			0			1,787,746	2,651,749
Adjusted weighted average share - diluted (in shares)	13,673,672			11,508,180			13,440,861	13,909,063
Diluted net income (loss) per share (in usd per share)	$ 0.03			$ (0.03)			$ 0.01	$ 0.03