Note 2 - Summary of Significant Accounting Policies - Principal Transaction Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Principal transactions	$ 1,344	$ (2,287)
Equity Securities [Member]
Principal transactions	295	(604)
Warrants and Other Investments [Member]
Principal transactions	944	(1,341)
Investment Partnerships [Member]
Principal transactions	$ 105	$ (342)

Amount of realized and unrealized gain (loss) resulting from the difference between acquisition price and selling price or fair value of trading assets and trading liabilities, and from the firm's direct investment activity, conducted separately from customer trading activities, including, but not limited to, investments in private equity, alternative investment products, real estate, and exchanges and memberships.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42567-110969

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