Note 9 - Stock-based Compensation - Stock Option Activity for Employees and Non-employees (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Options Outstanding, Beginning Balance (in shares)		114,931
Options Outstanding, Weighted Average Exercise Price, Beginning Balance (in dollars per share)		$ 204.76
Options Outstanding, Weighted-average Remaining Contractual Term (Year)		36 days	7 years 146 days
Options Outstanding, Aggregate Intrinsic Value			$ 404
Options Granted (in shares)		29,563	51,040
Options Granted, Weighted Average Exercise Price (in dollars per share)		$ 106.32
Options Exercised (in shares)
Options Exercised, Weighted Average Exercise Price (in dollars per share)
Options Forfeited (in shares)		(80,431)
Options Forfeited, Weighted Average Exercise Price (in dollars per share)		$ 124.40
Options Expired (in shares)		(63,951)
Options Expired, Weighted Average Exercise Price (in dollars per share)		$ 260.40
Options Outstanding, Ending Balance (in shares)		111	114,931
Options Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)		$ 218.40	$ 204.76
Options Exercisable (in shares)		111
Options Exercisable, Weighted Average Exercise Price (in dollars per share)		$ 218.40
Options Exercisable, Weighted-average Remaining Contractual Term (Year)		36 days
Options Exercisable, Aggregate Intrinsic Value
Options Vested or Expected to Vest (in shares)	[1]	111
Options Vested or Expected to Vest, Weighted Average Exercise Price (in dollars per share)	[1]	$ 218.40
Options Vested or Expected to Vest, Weighted-average Remaining Contractual Term (Year)	[1]	36 days
Options Vested or Expected to Vest, Aggregate Intrinsic Value	[1]

[1] Represents the number of vested options at December 31, 2019 plus the number of unvested options expected to vest based on the unvested options outstanding at December 31, 2019.