Note 3 - Periodic Pension Expense (Details Textual) - USD ($)	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Payment for Pension Benefits	$ 1,520,000	$ 500,000

Amount of payment for pension benefits. Excludes other postretirement benefits.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

Name:	us-gaap_PensionContributions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration