Note 7 - Deferred Revenue (Details Textual) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue, Remaining Performance Obligation, Percentage	75.00%		75.00%
Revenue, Remaining Performance Obligation, Amount	$ 13.5		$ 13.5
Deferred Revenue Costs Incurred	$ 2.3	$ 1.7	$ 6.5	$ 5.7

Percentage of remaining performance obligation to total remaining performance obligation not recognized as revenue.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant