Note 12 - Earnings Per Share (Details Textual)	12 Months Ended
Dec. 31, 2017
Common Class A [Member]
Common Stock, Voting Rights	1/20th of one vote per share
Common Class B [Member]
Common Stock, Voting Rights	One full vote per share

Description of voting rights of common stock. Includes eligibility to vote and votes per share owned. Include also, if any, unusual voting rights.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Name:	us-gaap_CommonStockVotingRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration