Note 13 - Capital Stock (Details Textual) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Jun. 08, 2023	Apr. 30, 2023	Apr. 30, 2022	Jan. 31, 2023	Apr. 30, 2023	Apr. 30, 2022	Jul. 31, 2020	Nov. 16, 2022	Oct. 31, 2022	Jul. 31, 2022	Nov. 26, 2021	May 17, 2021	May 14, 2021
Proceeds from Warrant Exercises					$ 6,206,000
Class of Warrant or Right, Outstanding (in shares)		4,792,586		4,792,586	4,792,586				4,837,586	3,615,454
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value		$ 9,666,000			$ 9,666,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value		8,903,000			8,903,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Unvested in Period, Intrinsic Value		763,000			763,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount		$ 1,219,000			1,219,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		10 months 20 days
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount		$ 879,000			$ 879,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year 4 months 24 days
Share-Based Payment Arrangement, Expense		$ 283,000	$ 183,000		$ 869,000	$ 560,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)		836,034			836,034
Performance-based Restriced Stock Units [Member]
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount		$ 683,000			$ 683,000					$ 981,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year 8 months 15 days
Share-Based Payment Arrangement, Expense		$ 99,000	$ 73,000		$ 298,000	$ 220,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)		734,582			734,582					734,582
Replacement Warrants [Member]
Class of Warrant or Right, Outstanding (in shares)		4,585,768			4,585,768
Replacement Warrants [Member] | Subsequent Event [Member]
Proceeds from Warrant Exercises	$ 1,060
Class of Warrant or Right, Exercised During Period (in shares)	928,188,000
Shelf 2021 [Member]
Stock Offering, Maximum Amount											$ 200,000,000	$ 200,000,000
May 17, 2021 At-the-market Offering [Member]
Stock Offering, Maximum Amount												$ 100,000,000
May 14, 2021 At-the-market Offering [Member]
Stock Offering, Maximum Amount													$ 100,000,000
Stock Issued During Period, Shares, New Issues (in shares)		0		6,201,553
Proceeds from Warrant Exercises							$ 0
Proceeds from Issuance of Common Stock, Net				$ 25,526,000
November 2021 At-the-market Offering [Member]
Stock Offering, Maximum Amount											$ 100,000,000
Shelf 2022 [Member]
Stock Offering, Maximum Amount								$ 300,000,000
November 2022 At-the-market Offering [Member]
Stock Offering, Maximum Amount								$ 300,000,000
Stock Issued During Period, Shares, New Issues (in shares)		2,912,000			8,969,700
Proceeds from Issuance of Common Stock, Net		$ 10,599			$ 32,893