Note 4 - Revenue From Contracts With Customers (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease), Total	$ 0

Amount of increase (decrease) in allowance for credit loss on accounts receivable.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration