Significant Accounting Policies - Calculation of Earnings Per Share (Details) - USD ($)	3 Months Ended				9 Months Ended
	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Basic loss per share computation
Net income (loss) attributable to common stockholders	$ (369,000)	$ 267,000	$ 483,000	$ (76,000)	$ 381,000	$ (844,000)
Weighted Average common shares - basic (in shares)	11,508,180			10,994,434	11,257,314	10,987,797
Basic net income (loss) per share (in dollars per share)	$ (0.03)			$ (0.01)	$ 0.03	$ (0.08)
Income (loss) available to common stockholders	$ (369,000)			$ (76,000)	$ 381,000	$ (844,000)
Incremental shares from assumed exercise of warrants and stock options (in shares)	0			0	2,651,749	0
Adjusted weighted average share - diluted (in shares)	11,508,180			10,994,434	13,909,063	10,987,797
Diluted net income (loss) per share (in usd per share)	$ (0.03)			$ (0.01)	$ 0.03	$ (0.08)