Note 11 - Equity Incentive Plans (Details Textual) - USD ($)							1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 24, 2020	Jul. 20, 2020	Jul. 09, 2020	Jun. 23, 2020	Jun. 15, 2020	Mar. 24, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Apr. 23, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)						2,610,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)						$ 1.70				$ 2.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)								6,320,530		6,320,530		1,811,652
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)								$ 2.27		$ 2.27		$ 2.74
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)										9 years 65 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value								$ 28,700,000		$ 28,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in shares)								2,539,452		2,539,452
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price (in dollars per share)								$ 2.79		$ 2.79
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term (Year)										8 years 328 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value								$ 10,800,000		$ 10,800,000
Proceeds from Stock Options Exercised										$ 402,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)										305,179	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value										$ 1,600,000
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount								$ 5,400,000		$ 5,400,000
Performance-based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)							411,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares)								411,000		411,000
Share-based Payment Arrangement, Expense								$ 101,000		$ 632,000
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 (Year)						24 years
Performance-based Options [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					900,000
Share Price (in dollars per share)					$ 2.46
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
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)					$ 2.46
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 (Year)					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								$ 915,000	$ 146,000	$ 3,871,000	$ 490,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)										$ 1.98	$ 0.55
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)										2 years 127 days
The 2019 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)				8,000,000									1,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)				10 years