Note 3 - Recent Accounting Pronouncements (Details Textual) - USD ($)		3 Months Ended
Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Equity Securities, FV-NI, Unrealized Gain (Loss), Total		$ (3,847,000)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect	$ 515,000
Accounting Standards Update 2016-01 [Member] \| Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 8,600,000

Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration