Note 9 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Anti-dilutive securities (in shares)	1,216	1,749
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)	400	622
Restricted Stock Units (RSUs) [Member]
Anti-dilutive securities (in shares)	716	748
Employee Stock Purchase Plan [Member]
Anti-dilutive securities (in shares)	100	379

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://www.xbrl.org/2003/role/disclosureRef
-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