Note 5 - Marketable Securities - Summary of Gross Unrealized Losses and Fair Values on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Less than 12 months, Fair value	$ 29,663	$ 22,852
Less than 12 months, Gross unrealized loss	(820)	(102)
12 months or greater, Fair value	8,219	14,231
12 months or greater, Gross unrealized loss	$ (136)	$ (32)

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

No definition available.

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