Note 2 - Summary of Significant Accounting Policies (Detail) (USD $)	1 Months Ended	12 Months Ended
	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Available-for-sale Securities, Fair Value Disclosure (in Dollars)		$ 102,956,000	$ 69,216,000
Available-for-sale Securities, Gross Unrealized Gain (Loss) (in Dollars)		52,464,000	24,532,000
Available-for-sale Securities, Gross Unrealized Gains (in Dollars)		54,653,000
Available-for-sale Securities, Gross Unrealized Losses (in Dollars)		2,189,000
Other than Temporary Impairment Losses, Investments (in Dollars)	2,855,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net (in Dollars)	1,720,000
Research and Development Expense, Software (Excluding Acquired in Process Cost) (in Dollars)		4,415,000	3,877,000
Weighted Average Number of Shares Outstanding, Basic and Diluted (in Shares)		1,380,746	1,380,746
Daily Journal Non-Consolidated [Member]
Management Incentive Plan Total Percentage Of Pre Tax Earnings		3.60%	3.55%
Management Incentive Plan Total Amount Paid (in Dollars)		513,500	548,480
Sustain Technologies, Inc. [Member]
Management Incentive Plan Total Percentage Of Pre Tax Earnings		8.23%	5.73%
Management Incentive Plan Total Amount Paid (in Dollars)		0	0
Daily Journal Consolidated [Member]
Management Incentive Plan Total Percentage Of Pre Tax Earnings		8.20%	8.20%
Management Incentive Plan Total Amount Paid (in Dollars)		936,840	1,090,760
Gross Unrealized Losses [Member]
Available-for-sale Securities, Gross Unrealized Losses (in Dollars)		1,209,000
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Estimated Useful Lives		5
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Estimated Useful Lives		39
Furniture, Office Equipment, and Software [Member] | Minimum [Member]
Property, Plant and Equipment, Estimated Useful Lives		3
Furniture, Office Equipment, and Software [Member] | Maximum [Member]
Property, Plant and Equipment, Estimated Useful Lives		5
Machinery and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Estimated Useful Lives		3
Machinery and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Estimated Useful Lives		10
Management Incentive Plan, Future Commitment [Member]
Other Accrued Liabilities (in Dollars)		4,200,000
Increase (Decrease) in Other Accrued Liabilities (in Dollars)		470,000
Gross Unrealized Gains [Member]
Available-for-sale Securities, Gross Unrealized Gain (Loss) (in Dollars)			28,983,000
Gross Unrealized Losses [Member]
Available-for-sale Securities, Gross Unrealized Gain (Loss) (in Dollars)			$ 4,451,000
Minimum [Member]
Property, Plant and Equipment, Estimated Useful Lives		3
Maximum [Member]
Property, Plant and Equipment, Estimated Useful Lives		39