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, 2018	$ 9,164	$ 56,439	$ (65)	$ (1,361)	$ (915)	$ 63,262
Balance (in Shares) at Apr. 30, 2018	9,163,940			297,083
Opening balance sheet Adjustment for ASU 2014-09			483			483
Contribution of stock to 401(k) plan		223		$ 189		412
Contribution of stock to 401(k) plan (in Shares)				(41,211)
Stock-based compensation expense		495		$ 5		$ 500
Stock-based compensation expense (in Shares)				(1,100)
Exercise of stock options and stock appreciation rights - net of		(326)		$ 326
Exercise of stock options and stock appreciation rights - net of (in Shares)				(71,111)		145,750
Change in unrealized gains and losses on marketable securities, net of taxes					171	$ 171
Foreign currency translation adjustment					790	790
Net loss			(2,529)			(2,529)
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		8,980,000
Contribution of stock to 401(k) plan		236		$ 181		$ 417
Contribution of stock to 401(k) plan (in Shares)				(39,403)
Stock-based compensation expense		304		$ 8		$ 312
Stock-based compensation expense (in Shares)				(1,850)
Exercise of stock options and stock appreciation rights - net of		(457)		$ 457
Exercise of stock options and stock appreciation rights - net of (in Shares)				(99,712)		171,250
Change in unrealized gains and losses on marketable securities, net of taxes					444	$ 444
Foreign currency translation adjustment						0
Net loss			(10,026)			(10,026)
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		8,980,000