Note 5 - Fair Value - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investments in U.S. Treasury Bills with maturities greater than 3 months	$ 115,829	$ 89,155
Investments in equity securities	249,669	196,583
Total investments in securities	365,498	285,738
Securities sold, not yet purchased	7,376	5,918
US Treasury Bill Securities [Member]
Investments in U.S. Treasury Bills with maturities greater than 3 months	115,829	89,155
Common Stock [Member]
Investments in equity securities	244,874	191,346
Mutual Fund [Member]
Investments in equity securities	1,450	1,186
Other Investments [Member]
Investments in equity securities	3,345	4,051
Fair Value, Recurring [Member]
Cash equivalents	259,247	315,017
Total investments in securities	365,498	285,738
Investments in affiliated registered investment companies	140,355	126,751
Investment, fair value	505,853	412,489
Total assets at fair value	765,100	727,506
Securities sold, not yet purchased	7,376	5,918
Total liabilities at fair value	7,376	5,918
Fair Value, Recurring [Member] \| US Treasury Bill Securities [Member]
Investments in U.S. Treasury Bills with maturities greater than 3 months	115,829	89,155
Fair Value, Recurring [Member] \| Common Stock [Member]
Investments in equity securities	244,874	191,346
Securities sold, not yet purchased	6,838	5,035
Fair Value, Recurring [Member] \| Mutual Fund [Member]
Investments in equity securities	1,450	1,186
Investments in affiliated registered investment companies	82,457	73,703
Fair Value, Recurring [Member] \| Other Investments [Member]
Investments in equity securities	3,345	4,051
Securities sold, not yet purchased	538	883
Fair Value, Recurring [Member] \| Closed End Funds [Member]
Investments in affiliated registered investment companies	48,042	44,692
Fair Value, Recurring [Member] \| Preferred Securities From Closed End Funds [Member]
Investments in affiliated registered investment companies	9,856	8,356
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash equivalents	259,247	315,017
Total investments in securities	361,867	281,651
Investments in affiliated registered investment companies	130,499	118,395
Investment, fair value	492,366	400,046
Total assets at fair value	751,613	715,063
Securities sold, not yet purchased	6,873	5,614
Total liabilities at fair value	6,873	5,614
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury Bill Securities [Member]
Investments in U.S. Treasury Bills with maturities greater than 3 months	115,829	89,155
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Common Stock [Member]
Investments in equity securities	242,017	187,963
Securities sold, not yet purchased	6,838	5,035
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Mutual Fund [Member]
Investments in equity securities	1,450	1,186
Investments in affiliated registered investment companies	82,457	73,703
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Investments [Member]
Investments in equity securities	2,571	3,347
Securities sold, not yet purchased	35	579
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Closed End Funds [Member]
Investments in affiliated registered investment companies	48,042	44,692
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Preferred Securities From Closed End Funds [Member]
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash equivalents	0	0
Total investments in securities	1,470	1,833
Investments in affiliated registered investment companies	0	0
Investment, fair value	1,470	1,833
Total assets at fair value	1,470	1,833
Securities sold, not yet purchased	503	304
Total liabilities at fair value	503	304
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury Bill Securities [Member]
Investments in U.S. Treasury Bills with maturities greater than 3 months	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Common Stock [Member]
Investments in equity securities	822	1,348
Securities sold, not yet purchased	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Mutual Fund [Member]
Investments in equity securities	0	0
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Investments [Member]
Investments in equity securities	648	485
Securities sold, not yet purchased	503	304
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Closed End Funds [Member]
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Preferred Securities From Closed End Funds [Member]
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Cash equivalents	0	0
Total investments in securities	2,161	2,254
Investments in affiliated registered investment companies	9,856	8,356
Investment, fair value	12,017	10,610
Total assets at fair value	12,017	10,610
Securities sold, not yet purchased	0	0
Total liabilities at fair value	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Treasury Bill Securities [Member]
Investments in U.S. Treasury Bills with maturities greater than 3 months	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Common Stock [Member]
Investments in equity securities	2,035	2,035
Securities sold, not yet purchased	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Mutual Fund [Member]
Investments in equity securities	0	0
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Investments [Member]
Investments in equity securities	126	219
Securities sold, not yet purchased	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Closed End Funds [Member]
Investments in affiliated registered investment companies	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Preferred Securities From Closed End Funds [Member]
Investments in affiliated registered investment companies	$ 9,856	$ 8,356

Fair value portion of asset recognized for present right to economic benefit.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of obligations incurred from short sales.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value portion of investments in an entity not consolidated. Includes, but is not limited to, investments in an entity that is affiliated with the reporting entity by means of direct or indirect ownership, an entity in which the reporting entity shares control of the entity with another party or group, an entity which the company has significant influence, but does not have control and subsidiaries that are not required to be consolidated and are accounted for using the equity or cost method.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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