Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Apr. 30, 2019	$ 9,164	$ 56,831	$ (2,111)	$ (841)	$ 46	$ 63,089
Balance (in Shares) at Apr. 30, 2019	9,163,940			183,661
Contribution of stock to 401(k) plan		74		$ 50		124
Contribution of stock to 401(k) plan (in Shares)				(10,906)
Stock-based compensation expense		80				80
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price		(189)		$ 189
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price (in Shares)				(41,325)
Other comprehensive income, net of tax					134	134
Net income (loss)			(591)			(591)
Balance at Jul. 31, 2019	$ 9,164	56,796	(2,702)	$ (602)	180	62,836
Balance (in Shares) at Jul. 31, 2019	9,163,940			131,430
Balance at Apr. 30, 2019	$ 9,164	56,831	(2,111)	$ (841)	46	63,089
Balance (in Shares) at Apr. 30, 2019	9,163,940			183,661
Net income (loss)						(7,046)
Balance at Jan. 31, 2020	$ 9,164	56,772	(9,157)	$ (258)	304	56,825
Balance (in Shares) at Jan. 31, 2020	9,163,940			56,381
Balance at Jul. 31, 2019	$ 9,164	56,796	(2,702)	$ (602)	180	62,836
Balance (in Shares) at Jul. 31, 2019	9,163,940			131,430
Contribution of stock to 401(k) plan		66		$ 39		105
Contribution of stock to 401(k) plan (in Shares)				(8,703)
Stock-based compensation expense		64				64
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price		(268)		$ 268
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price (in Shares)				(58,387)
Other comprehensive income, net of tax					72	72
Net income (loss)			(4,909)			(4,909)
Balance at Oct. 31, 2019	$ 9,164	56,658	(7,611)	$ (295)	252	58,168
Balance (in Shares) at Oct. 31, 2019	9,163,940			64,340
Contribution of stock to 401(k) plan		34		$ 28		62
Contribution of stock to 401(k) plan (in Shares)				(6,109)
Stock-based compensation expense		80		$ 9		89
Stock-based compensation expense (in Shares)				(1,850)
Other comprehensive income, net of tax					52	52
Net income (loss)			(1,546)			(1,546)
Balance at Jan. 31, 2020	$ 9,164	56,772	(9,157)	$ (258)	304	56,825
Balance (in Shares) at Jan. 31, 2020	9,163,940			56,381
Balance at Apr. 30, 2020	$ 9,164	56,914	(12,137)	$ (195)	490	54,236
Balance (in Shares) at Apr. 30, 2020	9,163,940			42,696
Contribution of stock to 401(k) plan		68		$ 68		136
Contribution of stock to 401(k) plan (in Shares)				(14,926)
Stock-based compensation expense		54				54
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price		(109)		$ 109
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price (in Shares)				(23,808)
Other comprehensive income, net of tax					171	171
Net income (loss)			(262)			(262)
Balance at Jul. 31, 2020	$ 9,164	56,927	(12,399)	$ (18)	661	54,335
Balance (in Shares) at Jul. 31, 2020	9,163,940			3,962
Balance at Apr. 30, 2020	$ 9,164	56,914	(12,137)	$ (195)	490	54,236
Balance (in Shares) at Apr. 30, 2020	9,163,940			42,696
Net income (loss)						(733)
Balance at Jan. 31, 2021	$ 9,194	57,192	(12,870)	$ (6)	451	53,961
Balance (in Shares) at Jan. 31, 2021	9,193,769			1,376
Balance at Jul. 31, 2020	$ 9,164	56,927	(12,399)	$ (18)	661	54,335
Balance (in Shares) at Jul. 31, 2020	9,163,940			3,962
Contribution of stock to 401(k) plan	$ 9	86				95
Contribution of stock to 401(k) plan (in Shares)	9,496
Stock-based compensation expense		73				73
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price	$ 3	(15)		$ 12		0
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price (in Shares)	2,654			(2,586)
Other comprehensive income, net of tax					(176)	(176)
Net income (loss)			329			329
Balance at Oct. 31, 2020	$ 9,176	57,071	(12,070)	$ (6)	485	54,656
Balance (in Shares) at Oct. 31, 2020	9,176,090			1,376
Contribution of stock to 401(k) plan	$ 6	63				69
Contribution of stock to 401(k) plan (in Shares)	6,116
Stock-based compensation expense	$ 4	65				69
Stock-based compensation expense (in Shares)	4,200
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price	$ 8	(7)				1
Exercise of stock options and stock appreciation rights - net of shares tendered for exercise price (in Shares)	7,363
Other comprehensive income, net of tax					(34)	(34)
Net income (loss)			(800)			(800)
Balance at Jan. 31, 2021	$ 9,194	$ 57,192	$ (12,870)	$ (6)	$ 451	$ 53,961
Balance (in Shares) at Jan. 31, 2021	9,193,769			1,376