Note 3 - Cash, Cash Equivalent and Marketable Investments (Details Textual) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax, Total	$ 27,000	$ 34,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant