Note 10 - Fair Value Measurements - Level 3 Investments (Details) - Auction Rate Securities [Member] $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Balance, auction rate securities	$ 5,256
Change in unrealized loss included in other comprehensive income (loss)	(9)
Balance, auction rate securities	$ 5,247

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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