Note 9 - Fair Value Disclosures - Fair Value Measurements on a Recurring Basis (Details) - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Investments-trading		$ 242,961,000	$ 307,852,000
Total other investments, at fair value		58,540,000	14,864,000
Investment securities sold, not yet purchased		44,439,000	77,947,000
Other investments sold, not yet purchased		7,415,000
Corporate Bonds and Redeemable Preferred Stock [Member]
Investments-trading		36,388,000	38,503,000
Investment securities sold, not yet purchased		29,206,000	58,083,000
Foreign Government Bonds [Member]
Investments-trading		659,000	844,000
Municipal Bonds [Member]
Investments-trading		19,400,000	13,737,000
Investment securities sold, not yet purchased		20,000	20,000
Certificates of Deposit [Member]
Investments-trading		70,000	841,000
Derivative [Member]
Investments-trading		13,717,000	3,686,000
Investment securities sold, not yet purchased		11,822,000	3,017,000
Other investments sold, not yet purchased		233,000
Equity Securities [Member]
Investments-trading		428,000	561,000
Total other investments, at fair value		51,593,000	8,875,000
Investment securities sold, not yet purchased		43,000
Other investments sold, not yet purchased		7,182,000
Residential Transition Loans [Member]
Total other investments, at fair value		2,300,000
Fair Value, Recurring [Member]
Investments-trading		242,961,000	307,852,000
Total other investments, at fair value		58,540,000	14,864,000
Investment securities sold, not yet purchased		44,439,000	77,947,000
Other investments sold, not yet purchased		7,415,000
Fair Value, Recurring [Member] | Corporate Bonds and Redeemable Preferred Stock [Member]
Investments-trading		36,388,000	38,503,000
Total other investments, at fair value		476,000	477,000
Fair Value, Recurring [Member] | Foreign Government Bonds [Member]
Investments-trading		659,000	844,000
Fair Value, Recurring [Member] | Municipal Bonds [Member]
Investments-trading		19,400,000	13,737,000
Investment securities sold, not yet purchased		20,000	20,000
Fair Value, Recurring [Member] | Certificates of Deposit [Member]
Investments-trading		70,000	841,000
Fair Value, Recurring [Member] | Derivative [Member]
Investments-trading		13,717,000	3,686,000
Investment securities sold, not yet purchased		11,822,000	3,017,000
Other investments sold, not yet purchased		233,000
Fair Value, Recurring [Member] | Equity Securities [Member]
Investments-trading		428,000	561,000
Total other investments, at fair value		51,593,000	8,875,000
Investment securities sold, not yet purchased		43,000
Other investments sold, not yet purchased		7,182,000
Fair Value, Recurring [Member] | Subordinated Debt [Member]
Total other investments, at fair value		1,519,000
Fair Value, Recurring [Member] | Residential Transition Loans [Member]
Total other investments, at fair value		2,300,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading		607,000	11,105,000
Investment securities sold, not yet purchased		3,391,000	16,827,000
Other investments sold, not yet purchased		7,415,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bonds and Redeemable Preferred Stock [Member]
Investments-trading
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Bonds [Member]
Investments-trading
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal Bonds [Member]
Investments-trading
Investment securities sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Investments-trading
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Investments-trading
Investment securities sold, not yet purchased
Other investments sold, not yet purchased		233,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Investments-trading
Total other investments, at fair value		17,422,000	2,009,000
Investment securities sold, not yet purchased		43,000
Other investments sold, not yet purchased		7,182,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Subordinated Debt [Member]
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential Transition Loans [Member]
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		242,354,000	296,747,000
Investment securities sold, not yet purchased		41,048,000	61,120,000
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bonds and Redeemable Preferred Stock [Member]
Investments-trading		36,388,000	38,503,000
Total other investments, at fair value		476,000	477,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Bonds [Member]
Investments-trading		659,000	844,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Investments-trading		19,400,000	13,737,000
Investment securities sold, not yet purchased		20,000	20,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Investments-trading		70,000	841,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Investments-trading		13,717,000	3,686,000
Investment securities sold, not yet purchased		11,822,000	3,017,000
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Investments-trading		428,000	561,000
Total other investments, at fair value		34,171,000	6,866,000
Investment securities sold, not yet purchased
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Subordinated Debt [Member]
Total other investments, at fair value		1,519,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential Transition Loans [Member]
Total other investments, at fair value		2,300,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
Investment securities sold, not yet purchased
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Bonds and Redeemable Preferred Stock [Member]
Investments-trading
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Bonds [Member]
Investments-trading
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal Bonds [Member]
Investments-trading
Investment securities sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Investments-trading
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Investments-trading
Investment securities sold, not yet purchased
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Investments-trading
Total other investments, at fair value
Investment securities sold, not yet purchased
Other investments sold, not yet purchased
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Subordinated Debt [Member]
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential Transition Loans [Member]
Total other investments, at fair value
Fair Value, Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Total other investments, at fair value	[1]	2,548,000	2,891,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member]
Investments-trading		162,031,000	196,146,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		162,031,000	196,146,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
US Government Agencies Debt Securities [Member] | Fair Value, Recurring [Member]
Investments-trading		6,904,000	14,680,000
US Government Agencies Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading
US Government Agencies Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		6,904,000	14,680,000
US Government Agencies Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
Investments-trading		14,000	15,000
Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading
Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		14,000	15,000
Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
US Treasury Securities [Member]
Investment securities sold, not yet purchased		3,348,000	16,827,000
US Treasury Securities [Member] | Fair Value, Recurring [Member]
Investments-trading		607,000	11,105,000
Investment securities sold, not yet purchased		3,348,000	16,827,000
US Treasury Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading		607,000	11,105,000
Investment securities sold, not yet purchased		3,348,000	16,827,000
US Treasury Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading
Investment securities sold, not yet purchased
US Treasury Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
Investment securities sold, not yet purchased
Asset-backed Securities [Member] | Fair Value, Recurring [Member]
Investments-trading		1,000	100,000
Asset-backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading
Asset-backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		1,000	100,000
Asset-backed Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
Small Business Administration Loans [Member] | Fair Value, Recurring [Member]
Investments-trading		2,742,000	27,634,000
Small Business Administration Loans [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investments-trading
Small Business Administration Loans [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investments-trading		2,742,000	27,634,000
Small Business Administration Loans [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investments-trading
Collateralized Loan Obligations [Member]
Total other investments, at fair value			2,522,000
Collateralized Loan Obligations [Member] | Fair Value, Recurring [Member]
Total other investments, at fair value			2,522,000
Collateralized Loan Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total other investments, at fair value
Collateralized Loan Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total other investments, at fair value
Collateralized Loan Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total other investments, at fair value			2,522,000
Residential Mortgage [Member]
Total other investments, at fair value		104,000	99,000
Residential Mortgage [Member] | Fair Value, Recurring [Member]
Total other investments, at fair value		104,000	99,000	[1]
Residential Mortgage [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total other investments, at fair value				[1]
Residential Mortgage [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total other investments, at fair value		104,000	99,000	[1]
Residential Mortgage [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total other investments, at fair value				[1]
Total Investments not Measured at NAV [Member] | Fair Value, Recurring [Member]
Total other investments, at fair value		55,992,000	11,973
Total Investments not Measured at NAV [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total other investments, at fair value		17,422,000	2,009
Total Investments not Measured at NAV [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total other investments, at fair value		38,570,000	7,442
Total Investments not Measured at NAV [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Total other investments, at fair value			2,522
Corporate Bonds and Redeemable Preferred Stock [Member]
Total other investments, at fair value		476,000	477,000
Corporate Bonds and Redeemable Preferred Stock [Member] | Fair Value, Recurring [Member]
Investment securities sold, not yet purchased		29,206,000	58,083,000
Corporate Bonds and Redeemable Preferred Stock [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities sold, not yet purchased
Corporate Bonds and Redeemable Preferred Stock [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities sold, not yet purchased		29,206,000	58,083,000
Corporate Bonds and Redeemable Preferred Stock [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities sold, not yet purchased

[1] As a practical expedient, the Company uses NAV per share (or its equivalent) to measure the fair value of its investments in the U.S. Insurance JV and the SPAC Fund. The U.S. Insurance JV invests in USD denominated debt issued by small insurance and reinsurance companies. The SPAC Fund invests in equity securities of SPACs. According to FASB ASC 820, these investments are not categorized within the valuation hierarchy.