Note 3 - Investments (Details Textual)		3 Months Ended
		Sep. 30, 2023 USD ($) $ / shares shares		Sep. 30, 2022 USD ($)	Sep. 30, 2023 $ / shares	Jun. 30, 2023 USD ($)	Mar. 31, 2021 $ / shares shares	Jan. 31, 2021 USD ($) $ / shares
Investment Owned, Fair Value		$ 18,300,000
Investment Owned, Cost		$ 26,200,000
Value of Fair Value Investments to Company Assets, Percent		33.80%
Equity Securities without Readily Determinable Fair Value, Amount		$ 1,613,000		$ 2,630,000		$ 2,388,000
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss	[1]	795,000				1,000,000
Equity Securities, FV-NI, Total		11,920,000				13,205,000
Debt Securities, Available-for-Sale, Total		6,343,000	[2]			7,008,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax		51,000		(115,000)
Investment Income, Net		(513,000)		(1,460,000)
Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss	[1]	205,000				232,000
Debt Securities, Held-to-Maturity, Credit Loss Expense (Reversal)		(27,000)	[3]	0
Debt Securities, Available-for-Sale, Periodic Principal Payments		750,000
Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Cumulative Amount		4,500,000				2,400,000
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Cumulative Amount		2,500,000
Realized Gain (Loss) on Principal Payment Proceeds		336,000		469,000
Equity Securities Without Readily Determinable Fair Values, Unrealized Gain (Loss)		775,000		1,800,000
U S Global Investors Funds [Member]
Investment Owned, Fair Value		11,500,000				12,400,000
HIVE Blockchain Technologies Ltd. [Member] | Convertible Securities [Member]
Investment Owned, Balance, Principal Amount								$ 15,000,000
HIVE Blockchain Technologies Ltd. [Member] | Warrants and Convertible Debentures [Member] | Fair Value, Inputs, Level 3 [Member] | Available-for-sale Securities and Equity Securities [Member]
Investment Owned, Fair Value		6,300,000				7,300,000
HIVE Blockchain Technologies Ltd. [Member] | Unsecured Convertible Debentures [Member]
Debt Securities, Available-for-Sale, Total		6,300,000				7,000,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax		$ 6,900,000
HIVE Blockchain Technologies Ltd. [Member] | Unsecured Convertible Debentures [Member] | Convertible Debt Securities [Member]
Debt Instrument, Interest Rate, Stated Percentage							8.00%
Debt Instrument, Convertible, Conversion Price (in dollars per share) | $ / shares		$ 11.7						$ 2.34
Investment Income, Net		$ 336,000		$ 469,000
HIVE Blockchain Technologies Ltd. [Member] | Common Shares Purchase Warrants [Member]
Investment, Common Share Purchase Warrants (in shares) | shares							5,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in CAD per share) | $ / shares					$ 15		$ 3
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares) | shares		5
Equity Securities, FV-NI, Total		$ 4,000				290,000
HIVE Blockchain Technologies Ltd. [Member] | Common Shares Purchase Warrants [Member] | Estimate of Fair Value Measurement [Member]
Equity Securities, FV-NI, Total		5,900,000
Debt Securities, Available-for-Sale, Total		16,000,000
HIVE Blockchain Technologies Ltd. [Member] | Convertible Securities [Member]
Investment Owned, Balance, Principal Amount		6,800,000
The Sonar Company [Member]
Equity Securities without Readily Determinable Fair Value, Amount		362,000				$ 362,000
Other Investments and Securities, at Cost		$ 175,000
Investment Owned, Direct Percentage		2.80%

[1] Held-to-maturity debt investments are carried at amortized cost, and the fair value is classified as Level 2 according to the fair value hierarchy.

[2] Principal payments of $750,000 are due quarterly with a final maturity date in January 2026.

[3] Represents the change in present value attributable to the passage of time included in interest income.