Note 10 - Equity Incentive Plans (Details Textual) - USD ($)		6 Months Ended
	Apr. 23, 2019	Jun. 30, 2022	Jun. 30, 2021	Aug. 04, 2022	Dec. 31, 2021	Jun. 16, 2021	Jun. 08, 2020
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)		14,305,918			10,216,106
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)		$ 4.76			$ 4.96
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)		8 years 7 months 20 days
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value		$ 7,000,000.0
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in shares)		4,941,521
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price (in dollars per share)		$ 3.33
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term (Year)		7 years 5 months 1 day
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value		$ 5,500,000
Proceeds from Stock Options Exercised		$ 79,000	$ 892,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period (in shares)		70,643	571,926
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value		$ 225,000	$ 3,200,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 3.98	$ 6.23
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		15,945,390			16,031,282
Restricted Stock Units (RSUs) [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		509,061
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)		4 years
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		507,472			0
Share-Based Payment Arrangement, Option [Member]
Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 38,700,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		3 years 2 months 26 days
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		14,305,918			10,216,106
The 2019 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	1,600,000					16,900,000	8,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
The 2019 Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)				28,900,000
The 2022 ESPP [Member] | Subsequent Event [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)				1,800,000