Note 10 - Summary of Stock Options (Details Textual) - USD ($)	1 Months Ended						3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jul. 31, 2019	Jun. 30, 2019	Apr. 30, 2019	Jan. 31, 2019	Jun. 30, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 01, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	50,471						50,471				50,471		40,144
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance	$ 298.99						$ 298.99				$ 298.99		$ 456
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 109 days		7 years 146 days
Stock Issued During Period, Shares, Restricted Stock Award, Gross						1,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance	3,432						3,432				3,432
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross											23,344
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate										0.00%	0.00%	0.00%
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate											0.00%
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 3,371,000						$ 3,371,000				$ 3,371,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition											2 years 73 days
Director [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross		378		525
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period				525
Director [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 38.08		$ 91
Consultant [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross			250
Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate										0.00%	0.00%	0.00%
The 2006 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	104						104				104
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	0						0				0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance	$ 992						$ 992				$ 992
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											3 years 109 days
The 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	50,367						50,367				50,367
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance	$ 297.56						$ 297.56				$ 297.56
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 109 days
Common Stock, Capital Shares Reserved for Future Issuance	11,770						11,770				11,770
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized					20,431
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized													49,140	69,571
Common Stock Shares Reserved For Future Issuance Percentage	18.00%						18.00%				18.00%
The 2013 Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period					3,625
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period							421				443
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period											0
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures, Total											0
The 2013 Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross										2,375	23,069	20,544
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value										$ 301.17	$ 117.86	$ 364.98
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period							0			0	0	0
The 2013 Plan [Member] | Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							0			100	275	2,123
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value										$ 283	$ 121.82	$ 241.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period							0			0	0	0
The 2013 Plan [Member] | Underwritten Public Offering [Member]
Minimum Gross Proceeds From Equity Offering Amount Used In Calculation Of Reserved Shares Percentage	$ 5,000,000
2017 Employee Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Employee Stock Purchase Plans							200	602	429
Shares Issued, Price Per Share	$ 3.75		$ 32.30				$ 3.75	$ 32.30	$ 79.88		$ 3.75
Employee Stock Ownership Plan (ESOP), Number of Suspense Shares	1,392						1,392				1,392
Employee Stock Ownership Plan (ESOP), Weighted Average Purchase Price of Shares Purchased							$ 13.16			$ 75	$ 2.12	$ 100
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate							0.00%			0.00%	0.00%	0.00%