Note 3 - Cash, Cash Equivalents and Investments (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2009
Auction Rate Securities Maturities	30 years
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1,381,000	$ 1,088,000
Gain (Loss) on Investments				$ 70,000
Percentage of Auction Rate Securities Redeemed at Par Value	87.00%
Auction Rate Securities [Member]
Redemption Auction Rate Securities	$ 0	0	$ 0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 300,000	$ 200,000

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

+ References + Details