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, 2017	$ 9,164	$ 55,767	$ 23,712	$ (1,592)	$ 2,281	$ 89,332
Balance (in Shares) at Apr. 30, 2017	9,163,940			347,422
Contribution of stock to 401(k) plan		219		$ 214		433
Contribution of stock to 401(k) plan (in Shares)				(46,628)
Stock-based compensation expense		457		$ 13		$ 470
Stock-based compensation expense (in Shares)				(2,850)
Exercise of stock options and stock appreciation rights - net of		(4)		$ 4
Exercise of stock options and stock appreciation rights - net of (in Shares)				(861)		3,500
Change in unrealized gains and losses on marketable securities, net of taxes					(1,292)	$ (1,292)
Foreign currency translation adjustment					(1,904)	(1,904)
Net Income (Loss)			(23,777)			(23,777)
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		8,867,000
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 Income (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