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Note 10 - Equity Incentive Plans (Details Textual) - USD ($)		3 Months Ended
	Apr. 23, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jun. 08, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)		7,764,164		6,813,033
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)		$ 3.28		$ 2.70
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)		8 years 10 months 28 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value		$ 23,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in shares)		3,007,780
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price (in dollars per share)		$ 2.65
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term (Year)		8 years 5 months 23 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value		$ 11,300,000
Proceeds from Stock Options Exercised		$ 231,000	$ 18,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)		207,730	23,606
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value		$ 1,100,000	$ 25,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		1,163,000
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 5.46
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			0
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 13,300,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		2 years 6 months 18 days
The 2019 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	1,600,000				8,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years