Note 6 - Stockholders' Equity and Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands							1 Months Ended								7 Months Ended	12 Months Ended
	Jun. 09, 2022	Jun. 30, 2021	Jun. 01, 2021	Feb. 05, 2021	Jan. 01, 2021	Jun. 01, 2019	Oct. 31, 2021	Jul. 31, 2021	Jun. 30, 2021	May 31, 2021	Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2017	Nov. 30, 2017	Feb. 04, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017	Nov. 30, 2021	Dec. 31, 2016	Dec. 31, 2014
Preferred Stock, Shares Authorized (in shares)																50,000,000	50,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)																$ 0.001	$ 0.001
Preferred Stock, Shares Outstanding, Ending Balance (in shares)																0	0
Common Stock, Shares Authorized (in shares)																500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)																$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock																$ 14,864	$ 56,697	$ 29,434
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																$ 2.05	$ 0
Class of Warrant or Right, Exercised During Period (in shares)																13,240
Class of Warrant or Right, Outstanding (in shares)																7,303,832	0
Proceeds from Warrant Exercises																$ 26	$ 4,217	244
Share-Based Payment Arrangement, Expense																5,191	14,601	10,075
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																$ 5,600
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)																2 years 3 months
Time-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value																	800	1,600
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value																$ 2,300	15,100	6,700
Share-Based Payment Arrangement, Expense																$ 4,467	9,235	8,739
Time-based Options [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage																25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)																1 year
Performance Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value																$ 800	2,500	5,500
Share-Based Payment Arrangement, Expense																233	4,840	133
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Expense																0	0	86
Restricted Stock Units (RSUs) [Member] | Granted in 2017 [Member] | Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)													68,800
Share-Based Payment Arrangement, Expense																0	$ 100	$ 300
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																0
Restricted Stock Units (RSUs) [Member] | Share-Based Payment Arrangement, Tranche One [Member] | Granted in 2017 [Member] | Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage						50.00%
Restricted Stock Units (RSUs) [Member] | Share-Based Payment Arrangement, Tranche Two [Member] | Granted in 2017 [Member] | Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage			50.00%
Modified Performance Options [Member]
Share-Based Payment Arrangement, Expense																$ 4,100
The 2017 Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)																			10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)													1,500,000						1,500,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)																1,188,657	1,022,002
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)													1,200,000						1,200,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent													4.00%						4.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																2,368,716
The 2017 Inducement Equity Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)														10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)														1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)										1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																1,053,767
The 2017 Inducement Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage														25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)														1 year
The 2017 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)													250,000						250,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)					383,250
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)													450,000						450,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent													1.50%						1.50%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																460,999
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)																188,097	91,378
Board of Directors Chairman [Member] | Loan Agreement [Member]
Long-Term Debt, Total		$ 0							$ 0
Board of Directors Chairman [Member] | Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount									$ 41,000
Chief Executive Officer [Member] | Restricted Stock Units (RSUs) [Member] | Granted in 2017 [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)													160,974
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares)																0
Share-Based Payment Arrangement, Expense																$ 0
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																0
Former Director [Member] | The 2017 Plan [Member] | Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)							10 years
Share-Based Payment Arrangement, Expense																$ 1,400
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Upon Resignation (Day)							90 days
Maximum [Member] | The 2017 Inducement Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)														10 years
Rights Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)												641,571				7,317,072
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 2.05											$ 7.01				$ 2.05
Warrants and Rights Outstanding, Term (Year)	5 years											5 years				5 years
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)	$ 0.01			$ 0.01												$ 0.01		$ 0.01
Class of Warrant or Right, Period of Written Notice for Exercise (Year)	30 years											30 days				30 years
Class of Warrant or Right, Percentage Required for Redemption	200.00%											200.00%				200.00%
Class of Warrant or Right, Exercise, Consecutive Trading Days (Year)	20 years											10 days				20 years
Period of Time Warrants Are Not Able to Be Redeemed (Month)	3 months											6 months
Class of Warrant or Right, Exercised During Period (in shares)				5,139											636,432	13,240
Class of Warrant or Right, Outstanding (in shares)																0	7,303,832
Proceeds from Warrant Exercises															$ 4,500
Rights Offering Warrants [Member] | Maximum [Member]
Additional Proceeds That May be Received Upon Exercise of Warrants	$ 15,000
Private Placement Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																						299,625
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																						$ 2.67
Warrants and Rights Outstanding, Term (Year)																						7 years
Class of Warrant or Right, Exercised During Period (in shares)											45,638
Stock Issued During Period, Shares, Exercise of Warrants (in shares)											40,563
Class of Warrant or Right, Unexercised and Expired (in shares)																				600
Class of Warrant or Right, Outstanding (in shares)																0
IPO Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																					574,985
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																					$ 5.00
Warrants and Rights Outstanding, Term (Year)																					5 years
Class of Warrant or Right, Exercised During Period (in shares)											85,385
Stock Issued During Period, Shares, Exercise of Warrants (in shares)											68,958
Class of Warrant or Right, Outstanding (in shares)																0
Rights Offering [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001											$ 0.001
Equity Offering, Units, Sale of Units (in shares)	7,317,072
Shares Issued, Price Per Share (in dollars per share)	$ 2.05
Number of Shares Per Unit Issued (in shares)	1
Number of Warrants Per Unit (in shares)	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Stock Issued During Period, Shares, New Issues (in shares)	7,317,072
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	7,317,072
Proceeds from Issuance of Common Stock	$ 15,000
Rights Offering [Member] | Board of Directors Chairman [Member]
Investment Owned, Percent of Net Assets	56.00%
Private Placement [Member] | Board of Directors Chairman [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001							$ 0.001
Shares Issued, Price Per Share (in dollars per share)		$ 16.40							$ 16.40
Stock Issued During Period, Shares, New Issues (in shares)		3,048,780
Proceeds from Issuance of Common Stock		$ 8,400						$ 8,400
Private Placement [Member] | Board of Directors Chairman [Member] | Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount		$ 41,000
ATM Offering [Member]
Shares Issued, Price Per Share (in dollars per share)																	$ 27.73
Stock Issued During Period, Shares, New Issues (in shares)																	288,490
Proceeds from Issuance of Common Stock																	$ 7,400
Equity Offering, Maximum Offering Amount															$ 60,000