Note 3 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure	$ 0	$ 0	$ 0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0	0
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure	0	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 0	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant