Document And Entity Information - shares	3 Months Ended
	Dec. 31, 2018	Jan. 31, 2019
Document Information [Line Items]
Entity Registrant Name	DAILY JOURNAL CORPORATION
Entity Central Index Key	0000783412
Trading Symbol	djco
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding (in shares)		1,380,746
Document Type	10-Q
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false