Document And Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2020	Nov. 30, 2020	Mar. 31, 2020
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	FY
Document Fiscal Year Focus	2020
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
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
City Area Code	213
Local Phone Number	229-5300
Title of 12(b) Security	Common Stock
Trading Symbol	DJCO
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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 Public Float			$ 275,783,000
Entity Common Stock, Shares Outstanding		1,380,746