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 Income (Loss) [Member]
Balance at Apr. 30, 2018	$ 27,253	$ 11	$ 100,011	$ (71,660)	$ (1,109)
Balance, shares at Apr. 30, 2018		10,799,895
Cash received pursuant to common stock subscription agreement	5,000		5,000
Stock-based compensation expense	347		347
Net loss	(5,030)			(5,030)
Foreign currency translation adjustments	(1,320)				(1,320)
Balance at Jul. 31, 2018	26,250	$ 11	105,358	(76,690)	(2,429)
Balance, shares at Jul. 31, 2018		10,799,895
Balance at Apr. 30, 2018	27,253	$ 11	100,011	(71,660)	(1,109)
Balance, shares at Apr. 30, 2018		10,799,895
Net loss	(12,290)
Foreign currency translation adjustments	(1,224)
Unrealized holding gains from available-for-sale securities	232
Balance at Jan. 31, 2019	104,033	$ 17	190,067	(83,950)	(2,101)
Balance, shares at Jan. 31, 2019		17,247,306
Balance at Jul. 31, 2018	26,250	$ 11	105,358	(76,690)	(2,429)
Balance, shares at Jul. 31, 2018		10,799,895
Issuance of common stock, net of issuance costs	82,811	$ 6	82,805
Issuance of common stock, net of issuance costs, shares		6,378,320
Issuance of common stock from exercise of stock options	25		25
Issuance of common stock from exercise of stock options, shares		4,452
Issuance of common stock from vesting of performance stock units, shares		42,500
Stock-based compensation expense	976		976
Net loss	(3,304)			(3,304)
Foreign currency translation adjustments	193				193
Balance at Oct. 31, 2018	106,951	$ 17	189,164	(79,994)	(2,236)
Balance, shares at Oct. 31, 2018		17,225,167
Issuance of common stock from exercise of stock options	106		106
Issuance of common stock from exercise of stock options, shares		22,139
Stock-based compensation expense	797		797
Net loss	(3,956)			(3,956)
Foreign currency translation adjustments	(97)				(97)
Unrealized holding gains from available-for-sale securities	232				232
Balance at Jan. 31, 2019	104,033	$ 17	190,067	(83,950)	(2,101)
Balance, shares at Jan. 31, 2019		17,247,306
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 available-for-sale 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	(22,532)
Foreign currency translation adjustments	548
Unrealized holding gains from available-for-sale securities	225
Reclassification adjustment for realized (gain) on available-for-sale securities included in net loss	(229)
Balance at Jan. 31, 2020	89,747	$ 18	206,119	(115,008)	(1,382)
Balance, shares at Jan. 31, 2020		17,845,599
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 from exercise of stock options	138		138
Issuance of common stock from exercise of stock options, 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 gains from available-for-sale 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
Issuance of common stock from exercise of stock options	47		47
Issuance of common stock from exercise of stock options, shares		11,473
Stock-based compensation expense	1,122		1,122
Net loss	(9,291)			(9,291)
Foreign currency translation adjustments	142				142
Unrealized holding gains from available-for-sale securities	40				40
Reclassification adjustment for realized (gain) on available-for-sale securities included in net loss	(100)				(100)
Balance at Jan. 31, 2020	$ 89,747	$ 18	$ 206,119	$ (115,008)	$ (1,382)
Balance, shares at Jan. 31, 2020		17,845,599