Note 13 - ASC 606 Revenue from contracts with customers - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investment banking	$ 18,117	$ 31,751
Intersegment Eliminations [Member]
Investment banking	(1,007)	(946)
Equity and Debt Origination [Member]
Investment banking	6,789	11,862
Equity and Debt Origination [Member] | Intersegment Eliminations [Member]
Investment banking
Strategic Advisory and Private Placements [Member]
Investment banking	5,090	8,800
Strategic Advisory and Private Placements [Member] | Intersegment Eliminations [Member]
Investment banking
Total Investment Banking Revenues [Member]
Investment banking	11,879	20,662
Total Investment Banking Revenues [Member] | Intersegment Eliminations [Member]
Investment banking
Brokerage Commissions [Member]
Investment banking	3,299	3,892
Brokerage Commissions [Member] | Intersegment Eliminations [Member]
Investment banking
Research Payments [Member]
Investment banking	1,209	985
Research Payments [Member] | Intersegment Eliminations [Member]
Investment banking
Trading Losses [Member]
Investment banking	27	(213)
Trading Losses [Member] | Intersegment Eliminations [Member]
Investment banking
Total Brokerage Revenue [Member]
Investment banking	4,535	4,664
Total Brokerage Revenue [Member] | Intersegment Eliminations [Member]
Investment banking
Management Service, Base [Member]
Investment banking	1,697	3,060
Management Service, Base [Member] | Intersegment Eliminations [Member]
Investment banking	(1,007)	(946)
Management Service, Incentive [Member]
Investment banking	6	3,365
Management Service, Incentive [Member] | Intersegment Eliminations [Member]
Investment banking
Total Asset Management Fees [Member]
Investment banking	1,703	6,425
Total Asset Management Fees [Member] | Intersegment Eliminations [Member]
Investment banking	(1,007)	(946)
Broker Dealer [Member]
Investment banking	16,414	25,326
Broker Dealer [Member] | Equity and Debt Origination [Member]
Investment banking	6,789	11,862
Broker Dealer [Member] | Strategic Advisory and Private Placements [Member]
Investment banking	5,090	8,800
Broker Dealer [Member] | Total Investment Banking Revenues [Member]
Investment banking	11,879	20,662
Broker Dealer [Member] | Brokerage Commissions [Member]
Investment banking	3,299	3,892
Broker Dealer [Member] | Research Payments [Member]
Investment banking	1,209	985
Broker Dealer [Member] | Trading Losses [Member]
Investment banking	27	(213)
Broker Dealer [Member] | Total Brokerage Revenue [Member]
Investment banking	4,535	4,664
Broker Dealer [Member] | Management Service, Base [Member]
Investment banking
Broker Dealer [Member] | Management Service, Incentive [Member]
Investment banking
Broker Dealer [Member] | Total Asset Management Fees [Member]
Investment banking
Asset Management Fee Income [Member]
Investment banking	2,710	4,086
Asset Management Fee Income [Member] | Equity and Debt Origination [Member]
Investment banking
Asset Management Fee Income [Member] | Strategic Advisory and Private Placements [Member]
Investment banking
Asset Management Fee Income [Member] | Total Investment Banking Revenues [Member]
Investment banking
Asset Management Fee Income [Member] | Brokerage Commissions [Member]
Investment banking
Asset Management Fee Income [Member] | Research Payments [Member]
Investment banking
Asset Management Fee Income [Member] | Trading Losses [Member]
Investment banking
Asset Management Fee Income [Member] | Total Brokerage Revenue [Member]
Investment banking
Asset Management Fee Income [Member] | Management Service, Base [Member]
Investment banking	2,704	4,006
Asset Management Fee Income [Member] | Management Service, Incentive [Member]
Investment banking	6	80
Asset Management Fee Income [Member] | Total Asset Management Fees [Member]
Investment banking	2,710	4,086
Asset Management Investment Income [Member]
Investment banking		3,285
Asset Management Investment Income [Member] | Equity and Debt Origination [Member]
Investment banking
Asset Management Investment Income [Member] | Strategic Advisory and Private Placements [Member]
Investment banking
Asset Management Investment Income [Member] | Total Investment Banking Revenues [Member]
Investment banking
Asset Management Investment Income [Member] | Brokerage Commissions [Member]
Investment banking
Asset Management Investment Income [Member] | Research Payments [Member]
Investment banking
Asset Management Investment Income [Member] | Trading Losses [Member]
Investment banking
Asset Management Investment Income [Member] | Total Brokerage Revenue [Member]
Investment banking
Asset Management Investment Income [Member] | Management Service, Base [Member]
Investment banking
Asset Management Investment Income [Member] | Management Service, Incentive [Member]
Investment banking		3,285
Asset Management Investment Income [Member] | Total Asset Management Fees [Member]
Investment banking		3,285
Asset Management [Member]
Investment banking	2,710	7,371
Asset Management [Member] | Equity and Debt Origination [Member]
Investment banking
Asset Management [Member] | Strategic Advisory and Private Placements [Member]
Investment banking
Asset Management [Member] | Total Investment Banking Revenues [Member]
Investment banking
Asset Management [Member] | Brokerage Commissions [Member]
Investment banking
Asset Management [Member] | Research Payments [Member]
Investment banking
Asset Management [Member] | Trading Losses [Member]
Investment banking
Asset Management [Member] | Total Brokerage Revenue [Member]
Investment banking
Asset Management [Member] | Management Service, Base [Member]
Investment banking	2,704	4,006
Asset Management [Member] | Management Service, Incentive [Member]
Investment banking	6	3,365
Asset Management [Member] | Total Asset Management Fees [Member]
Investment banking	2,710	7,371
Corporate Segment [Member]
Investment banking
Corporate Segment [Member] | Equity and Debt Origination [Member]
Investment banking
Corporate Segment [Member] | Strategic Advisory and Private Placements [Member]
Investment banking
Corporate Segment [Member] | Total Investment Banking Revenues [Member]
Investment banking
Corporate Segment [Member] | Brokerage Commissions [Member]
Investment banking
Corporate Segment [Member] | Research Payments [Member]
Investment banking
Corporate Segment [Member] | Trading Losses [Member]
Investment banking
Corporate Segment [Member] | Total Brokerage Revenue [Member]
Investment banking
Corporate Segment [Member] | Management Service, Base [Member]
Investment banking
Corporate Segment [Member] | Management Service, Incentive [Member]
Investment banking
Corporate Segment [Member] | Total Asset Management Fees [Member]
Investment banking