Document And Entity Information - shares	9 Months Ended
	Jun. 30, 2021	Jul. 31, 2021
Document Information [Line Items]
Entity Central Index Key	0000783412
Entity Registrant Name	DAILY JOURNAL CORPORATION
Amendment Flag	false
Current Fiscal Year End Date	--09-30
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	0-14665
Entity Incorporation, State or Country Code	SC
Entity Tax Identification Number	95-4133299
Entity Address, Address Line One	915 East First Street
Entity Address, City or Town	Los Angeles
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	90012-4050
City Area Code	213
Local Phone Number	229-5300
Title of 12(b) Security	Common Stock
Trading Symbol	DJCO
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,380,746