Note 4 - Fair Value Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Assets:
Marketable securities owned		$ 78,557	$ 18,484
Liabilities
Marketable securities sold, but not yet purchased		2,696	4,626
Reported Value Measurement [Member]
Assets:
Cash and cash equivalents		41,909	70,927
Restricted cash and deposits		1,221	61,881
Marketable securities owned		92,190	18,874
Other investments		8,349	490
Other investments measured at net asset value	[1]	9,763	9,423
Loans held for investment, net of allowance for loan losses		4,962	29,608
Total assets:		158,394	1,352,666
Loans collateralizing asset-backed securities issued, net of allowance for loan losses			1,161,463
Liabilities
Marketable securities sold, but not yet purchased		2,696	4,626
Notes payable		829	829
Bond payable		83,600	83,497
Total liabilities:		87,125	1,223,794
Asset-backed securities issued, net of debt issuance costs			1,112,342
CLO VI warehouse credit facility			22,500
Estimate of Fair Value Measurement [Member]
Assets:
Cash and cash equivalents		41,909	70,927
Restricted cash and deposits		1,221	61,881
Marketable securities owned		91,679	18,874
Other investments		8,349	490
Other investments measured at net asset value	[1]
Loans held for investment, net of allowance for loan losses		4,986	28,764
Total assets:		148,144	1,307,419
Loans collateralizing asset-backed securities issued, net of allowance for loan losses			1,126,483
Liabilities
Marketable securities sold, but not yet purchased		2,696	4,626
Notes payable		829	829
Bond payable		86,659	78,642
Total liabilities:		90,184	1,198,274
Asset-backed securities issued, net of debt issuance costs			1,091,677
CLO VI warehouse credit facility			22,500
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Cash and cash equivalents		41,909	70,927
Restricted cash and deposits		1,221	61,881
Marketable securities owned		15,717	18,874
Other investments
Other investments measured at net asset value	[1]
Loans held for investment, net of allowance for loan losses
Total assets:		58,847	151,682
Loans collateralizing asset-backed securities issued, net of allowance for loan losses
Liabilities
Marketable securities sold, but not yet purchased		2,696	4,626
Notes payable
Bond payable
Total liabilities:		2,696	4,626
Asset-backed securities issued, net of debt issuance costs
CLO VI warehouse credit facility
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Cash and cash equivalents
Restricted cash and deposits
Marketable securities owned
Other investments			490
Other investments measured at net asset value	[1]
Loans held for investment, net of allowance for loan losses		2,318	26,188
Total assets:		2,318	1,151,988
Loans collateralizing asset-backed securities issued, net of allowance for loan losses			1,125,310
Liabilities
Marketable securities sold, but not yet purchased
Notes payable
Bond payable		86,659	78,642
Total liabilities:		86,659	1,192,819
Asset-backed securities issued, net of debt issuance costs			1,091,677
CLO VI warehouse credit facility			22,500
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Cash and cash equivalents
Restricted cash and deposits
Marketable securities owned		75,962
Other investments		8,349
Other investments measured at net asset value	[1]
Loans held for investment, net of allowance for loan losses		2,668	2,576
Total assets:		86,979	3,749
Loans collateralizing asset-backed securities issued, net of allowance for loan losses			1,173
Liabilities
Marketable securities sold, but not yet purchased
Notes payable		829	829
Bond payable
Total liabilities:		$ 829	829
Asset-backed securities issued, net of debt issuance costs
CLO VI warehouse credit facility

[1] In accordance with ASC 820-10, certain investments that are measured at fair value using the net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. The carrying values of these lines reconciles to the parenthetical disclosure of other investments on the Consolidated Statements of Financial Condition.