Note 10 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Antidilutive securities (in shares)	3,346,091	646,273
Share-based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	848,148	616,567
Restricted Stock Units (RSUs) [Member]
Antidilutive securities (in shares)	62,135	29,706
Warrant [Member]
Antidilutive securities (in shares)	2,435,808

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