Note 6 - Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments in equity securities	$ 14,754	$ 10,993
Mutual funds	9,852	7,962
Fair Value, Inputs, Level 1 [Member]
Investments in equity securities	14,754	10,993
Mutual funds	9,852	7,962
Fair Value, Inputs, Level 2 [Member]
Investments in equity securities
Mutual funds
Fair Value, Inputs, Level 3 [Member]
Investments in equity securities
Mutual funds

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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