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Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 28, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Available-for-sale Securities, Total |  | $ 212,296,000 |  |  |  | $ 212,296,000 | $ 229,265,000 |
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax, Total |  | 158,407,000 |  |  |  | 158,407,000 | 165,872,000 |
Deferred Tax Liabilities, Investments |  | 42,151,000 |  |  |  | 42,151,000 | 64,550,000 |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities |  | 4,560,000 |  |  |  | 4,560,000 | 0 |
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax, Total |  |  |  |  |  | 3,350,000 |  |
Finite-Lived Intangible Assets, Net, Ending Balance |  |  |  |  |  |  | 3,058,000 |
Finite-Lived Intangible Assets, Accumulated Amortization |  | 24,475,000 |  |  |  | $ 24,475,000 | 21,417,000 |
Finite-Lived Intangible Asset, Useful Life |  |  |  |  |  | 5 years |  |
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months |  | 3,058,000 |  |  |  | $ 3,058,000 |  |
Amortization of Intangible Assets, Total |  |  |  |  |  | 3,058,000 | 4,895,000 | 5,037,000
Goodwill, Ending Balance |  | 13,400,000 |  |  |  | 13,400,000 | 13,400,000 |
Depreciation, Total |  |  |  |  |  | $ 620,000 | $ 691,000 | $ 672,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period |  |  |  |  |  | 10 years |  |
Weighted Average Number of Shares Outstanding, Basic and Diluted |  |  |  |  |  | 1,380,746 | 1,380,746 | 1,380,746
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets |  | $ 19,960,000 |  |  |  | $ 19,960,000 |  |
Measurement Input, Discount Rate [Member] |  |  |  |  |  |  |  |
Incentive Plan Future Commitment, Measurement Input |  | 6.00% |  |  |  | 6.00% |  |
Management Incentive Plan, Future Commitment [Member] |  |  |  |  |  |  |  |
Other Accrued Liabilities |  | $ 170,000 |  |  |  | $ 170,000 | $ 135,000 |
Increase (Decrease) in Other Accrued Liabilities |  |  |  |  |  | $ 35,000 | $ 75,000 |
Other Accrued Liabilities Impact on Earnings Per Share |  |  |  |  |  | $ 0.03 | $ 0.06 |
Daily Journal Non-Consolidated [Member] |  |  |  |  |  |  |  |
Management Incentive Plan Total Percentage of Pre Tax Earnings |  |  |  |  |  | 6.09% | 5.12% | 4.49%
Management Incentive Plan Total Amount Paid |  |  |  |  |  | $ 367,400 | $ 268,250 | $ 271,350
Journal Technologies [Member] |  |  |  |  |  |  |  |
Management Incentive Plan Total Percentage of Pre Tax Earnings |  |  |  |  |  | 8.72% | 8.53% | 8.30%
Management Incentive Plan Total Amount Paid |  |  |  |  |  | $ 0 | $ 0 | $ 0
Daily Journal Consolidated [Member] |  |  |  |  |  |  |  |
Management Incentive Plan Total Percentage of Pre Tax Earnings |  |  |  |  |  | 8.20% | 8.20% | 8.20%
Management Incentive Plan Total Amount Paid |  |  |  |  |  | $ 0 | $ 0 | $ 0
Product Concentration Risk [Member] | Sales Revenue, Net [Member] |  |  |  |  |  |  |  |
Concentration Risk, Percentage |  |  |  |  |  | 58.00% | 58.00% | 56.00%
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 |  |
Prepaid Expenses and Other Current Assets [Member] | New Dawn [Member] |  |  |  |  |  |  |  |
Contract with Customer, Asset, Net, Current, Total |  | 0 |  |  |  | $ 0 | $ 350,000 |
Customer Relationships [Member] |  |  |  |  |  |  |  |
Finite-Lived Intangible Assets, Net, Ending Balance |  | 0 |  |  |  | 0 | 2,776,000 |
Finite-Lived Intangible Assets, Accumulated Amortization |  | 21,950,000 |  |  |  | 21,950,000 | 19,174,000 |
Developed Technology Rights [Member] |  |  |  |  |  |  |  |
Finite-Lived Intangible Assets, Net, Ending Balance |  | 0 |  |  |  | 0 | 282,000 |
Finite-Lived Intangible Assets, Accumulated Amortization |  | $ 2,525,000 |  |  |  | $ 2,525,000 | $ 2,243,000 |
Bonds [Member] |  |  |  |  |  |  |  |
Proceeds from Sale of Available-for-sale Securities, Total | $ 8,125,000 |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Realized Gain (Loss), Total | 3,180,000 |  |  |  |  |  |  |
Reclassification of Tax Effect from AOCI to Retained Earnings | $ 30,000 |  |  |  |  |  |  |

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