Note 2 - Revenue (Details Textual) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018
Deferred Revenue [Member]
Deposit Liability, Current	$ 4.8	$ 3.8

The current portion, due within one year or one operating cycle, if longer, of deposits held other than customer deposits.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DepositLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant