Note 2 - Investments - Current Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized cost	$ 33,778	$ 29,166
Unrealized loss	(20)	(49)
Fair market value	33,758	29,117
Corporate Bond Securities [Member]
Amortized cost	33,778	22,100
Unrealized loss	(20)	(46)
Fair market value	33,758	22,054
Municipal Bonds [Member]
Amortized cost		3,727
Unrealized loss		(1)
Fair market value		3,726
US Government Agencies Debt Securities [Member]
Amortized cost		3,339
Unrealized loss		(2)
Fair market value		$ 3,337

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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