Condensed Consolidated Statement of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Apr. 30, 2019	$ 96,738	$ 17	$ 191,123	$ (92,476)	$ (1,926)
Balance, shares at Apr. 30, 2019		17,277,750
Issuance of common stock, net of issuance costs	11,422	$ 1	11,421
Issuance of common stock, net of issuance costs, shares		527,221
Issuance of common stock from equity incentive plans	32		32
Issuance of common stock from equity incentive plans, shares		10,522
Stock-based compensation expense	1,074		1,074
Net loss	(7,338)			(7,338)
Foreign currency translation adjustments	(89)				(89)
Unrealized holding gains from marketable securities, net of reclassification for realized gains	28				28
Balance at Jul. 31, 2019	101,867	$ 18	203,650	(99,814)	(1,987)
Balance, shares at Jul. 31, 2019		17,815,493
Balance at Apr. 30, 2019	96,738	$ 17	191,123	(92,476)	(1,926)
Balance, shares at Apr. 30, 2019		17,277,750
Net loss	(13,241)
Foreign currency translation adjustments	406
Unrealized holding losses from marketable securities	56
Balance at Oct. 31, 2019	97,787	$ 18	204,950	(105,717)	(1,464)
Balance, shares at Oct. 31, 2019		17,834,126
Balance at Jul. 31, 2019	101,867	$ 18	203,650	(99,814)	(1,987)
Balance, shares at Jul. 31, 2019		17,815,493
Issuance of common stock, net of issuance costs	138		138
Issuance of common stock, net of issuance costs, shares		18,633
Stock-based compensation expense	1,162		1,162
Net loss	(5,903)			(5,903)
Foreign currency translation adjustments	495				495
Unrealized holding losses from marketable securities	28
Unrealized holding gains from marketable securities, net of reclassification for realized gains	28				28
Balance at Oct. 31, 2019	97,787	$ 18	204,950	(105,717)	(1,464)
Balance, shares at Oct. 31, 2019		17,834,126
Balance at Apr. 30, 2020	83,752	$ 18	207,208	(121,592)	(1,882)
Balance, shares at Apr. 30, 2020		17,845,599
Issuance of common stock from exercise of stock options	46		46
Issuance of common stock from exercise of stock options, shares		34,815
Stock-based compensation expense	1,188		1,188
Net loss	(10,814)			(10,814)
Foreign currency translation adjustments	338				338
Unrealized holding losses from marketable securities	(5)				(5)
Reclassification adjustment for realized (gain) on marketable securities included in net loss	(70)				(70)
Balance at Jul. 31, 2020	74,435	$ 18	208,442	(132,406)	(1,619)
Balance, shares at Jul. 31, 2020		17,880,414
Balance at Apr. 30, 2020	83,752	$ 18	207,208	(121,592)	(1,882)
Balance, shares at Apr. 30, 2020		17,845,599
Net loss	(21,241)
Foreign currency translation adjustments	211
Unrealized holding losses from marketable securities	(169)
Reclassification adjustment for realized (gain) on marketable securities included in net loss	(116)
Balance at Oct. 31, 2020	64,980	$ 18	209,750	(142,832)	(1,956)
Balance, shares at Oct. 31, 2020		17,915,515
Balance at Jul. 31, 2020	74,435	$ 18	208,442	(132,406)	(1,619)
Balance, shares at Jul. 31, 2020		17,880,414
Issuance of common stock from exercise of stock options	60		60
Issuance of common stock from exercise of stock options, shares		35,101
Stock-based compensation expense	1,248		1,248
Net loss	(10,426)			(10,426)
Foreign currency translation adjustments	(127)				(127)
Unrealized holding losses from marketable securities	(164)				(164)
Reclassification adjustment for realized (gain) on marketable securities included in net loss	(46)				(46)
Balance at Oct. 31, 2020	$ 64,980	$ 18	$ 209,750	$ (142,832)	$ (1,956)
Balance, shares at Oct. 31, 2020		17,915,515