Note 13 - Equity Incentive Plans (Details Textual) - USD ($)							1 Months Ended		9 Months Ended	12 Months Ended
	Jul. 24, 2020	Jul. 20, 2020	Jul. 09, 2020	Jun. 15, 2020	Mar. 24, 2020	Apr. 23, 2019	Mar. 31, 2020	Nov. 30, 2016	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 23, 2020	Dec. 31, 2017	Jul. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)										1,230,863	295,180	200,650
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)										6,813,033	1,811,652	865,163		304,850
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)										$ 2.70	$ 2.74	$ 8.13		$ 9.50
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)										8 years 361 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value										$ 22,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in shares)										6,502,213
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price (in dollars per share)										$ 2.68
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term (Year)										8 years 354 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value										$ 21,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares)										2,886,541
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price (in dollars per share)										$ 2.65
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year)										8 years 237 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value										$ 9,900,000
Share Price (in dollars per share)							$ 1.70			$ 5.71
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value										$ 2,200,000		$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)										414,676	0	2,013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					2,610,000					5,579,800	1,791,030	431,100
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)					$ 1.70					$ 2.66	$ 0.67	$ 5.17
Performance-based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares)							411,000
Share-based Payment Arrangement, Expense									$ 632,000
Share-based Payment Arrangement, Reversal of Expense										$ 632,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations, Total (in shares)										411,000
March Option Awards [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 (Month)					2 years
Performance-based Options [Member] | Chief Executive Officer [Member]
Share Price (in dollars per share)				$ 2.46
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)				900,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate				105.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate				0.35%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate				0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)				5 years 83 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)				$ 0.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Grant Date Fair Value				$ 279,000
Performance-based Options [Member] | Share-based Payment Arrangement, Tranche One [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				33.33%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Minimum Closing Price for Ten Consecutive Trading Days (in dollars per share)			$ 5	$ 5
Performance-based Options [Member] | Share-based Payment Arrangement, Tranche Two [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				33.33%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Minimum Closing Price for Ten Consecutive Trading Days (in dollars per share)		$ 7.50		$ 7.50
Performance-based Options [Member] | Share-based Payment Arrangement, Tranche Three [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				33.33%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Minimum Closing Price for Ten Consecutive Trading Days (in dollars per share)	$ 10			$ 10
Time-based Options [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)				845,280
Time-based Options [Member] | Share-based Payment Arrangement, Tranche One [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				25.00%
Time-based Options [Member] | Share-based Payment Arrangement, Tranche Two [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				75.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month)				3 years
Time-based Options [Member] | Share-based Payment Arrangement, Tranche Three [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Accelerated Vesting Percentage				50.00%
Performance-based Options and Time-based Options [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)				$ 2.46
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense										$ 4,358,000	$ 627,000	$ 539,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)										$ 2.49	$ 0.48	$ 3.59
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount										$ 8,200,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)										2 years 113 days
The 2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)															0
The 2016 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)						0
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)								10 years
The 2019 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)						1,600,000							8,000,000