Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)	1 Months Ended		12 Months Ended
	Mar. 31, 2023	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Restricted Cash and Cash Equivalents			$ 2,100,000	$ 2,045,000
Net income (loss)			21,452,000	(75,624,000)
Net unrealized gains (losses) on investments			17,024,000	(123,401,000)
Net Income (Loss) Attributable to Parent			(21,452,000)	75,624,000
Unrealized Gain (Loss) on Investments			(17,024,000)	123,401,000
Equity Securities, FV-NI, Current			303,128,000	275,529,000
Equity Securities, FV-NI, Unrealized Gain (Loss)			137,716,000	120,692,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Tax			36,260,000	32,120,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale			2,826,000	80,570,000
Debt Securities, Available-for-Sale, Realized Gain (Loss)			422,000	14,249,000
Payments to Acquire Marketable Securities			10,001,000	117,678,000
Proceeds from Issuance of Debt			6,011,000	43,014,000
Repayments of Debt			6,011,000
Investment Margin Account			75,000,000	75,000,000
Dividend Income, Operating, Paid in Kind	$ 2,978,000
Depreciation			$ 279,000	$ 379,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period				10 years
Common Stock, Shares, Outstanding				1,377,026
Weighted Average Number of Shares Outstanding, Basic			1,377,026	1,379,655
Operating Lease, Right-of-Use Asset			$ 95,000	$ 104,000
Accrued Liabilities [Member]
Operating Lease, Liability			95,000	$ 104,000
Accrued Liabilities, Current and Noncurrent [Member]
Operating Lease, Liability, Noncurrent			$ 44,000		$ 22,000
Director [Member]
Receipt of Donated Treasury Stock, Shares		3,720
Receipt of Donated Treasury Stock, Value		$ 1,000,000
Measurement Input, Discount Rate [Member]
Incentive Plan Future Commitment, Measurement Input			6.00%	6.00%
Management Incentive Plan, Future Commitment [Member]
Other Accrued Liabilities			$ 4,230,000	$ 4,525,000
Increase (Decrease) in Other Accrued Liabilities			$ 295,000	$ (1,245,000)
Other Accrued Liabilities Impact on Earnings Per Share			$ 21	$ (90)
Increase (Decrease) in Other Accrued Liabilities			$ (295,000)	$ 1,245,000
Other Accrued Liabilities Impact on Earnings Per Share			$ (21)	$ 90
Daily Journal Non-Consolidated [Member]
Management Incentive Plan Total Percentage of Pre Tax Earnings			4.71%	5.15%
Management Incentive Plan Total Amount Paid			$ 388,450	$ 474,300
Journal Technologies [Member]
Management Incentive Plan Total Percentage of Pre Tax Earnings			22.20%	21.70%
Management Incentive Plan Total Amount Paid			$ 1,491,840	$ 455,700
Daily Journal Consolidated [Member]
Management Incentive Plan Total Percentage of Pre Tax Earnings			8.86%	11.69%
Management Incentive Plan Total Amount Paid			$ 1,260,800	$ 1,295,540
Product Concentration Risk [Member] | Revenue Benchmark [Member] | License [Member]
Concentration Risk, Percentage			76.00%	71.00%
Minimum [Member]
Property, Plant and Equipment, Useful Life			3 years
Minimum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment, Useful Life			5 years
Minimum [Member] | Furniture, Office Equipment, and Software [Member]
Property, Plant and Equipment, Useful Life			3 years
Minimum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment, Useful Life			3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life			39 years
Maximum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment, Useful Life			39 years
Maximum [Member] | Furniture, Office Equipment, and Software [Member]
Property, Plant and Equipment, Useful Life			5 years
Maximum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment, Useful Life			10 years