Note 3 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Antidilutive securities (in shares)	1,468,105	717,431
Employee and Non-employee Stock Options [Member]
Antidilutive securities (in shares)	639,359	480,035
Common Stock Purchase Warrants [Member]
Antidilutive securities (in shares)	807,563	216,213
Deferred Share Units [Member]
Antidilutive securities (in shares)	21,183	21,183

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration