Document and Entity Information - shares	9 Months Ended
	Mar. 31, 2020	May 06, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	QNST
Entity Registrant Name	QuinStreet, Inc.
Entity Central Index Key	0001117297
Current Fiscal Year End Date	--06-30
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity File Number	001-34628
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		51,952,548
Entity Tax Identification Number	77-0512121
Entity Address, Address Line One	950 Tower Lane
Entity Address, Address Line Two	6th Floor
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	578-7700
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.001 per share