Note 8 - Preferred Stock (Details Textual) - shares	Apr. 15, 2019	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock, Shares Authorized		10,000,000	10,000,000
Preferred Stock, Shares Outstanding, Ending Balance		0	0
Subsequent Event [Member]
Preferred Stock, Shares Outstanding, Ending Balance	0

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PreferredStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant