Document and Entity Information - USD ($)	12 Months Ended
	Jun. 30, 2020	Aug. 24, 2020	Dec. 31, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	QNST
Entity Registrant Name	QuinStreet, Inc.
Entity Central Index Key	0001117297
Current Fiscal Year End Date	--06-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		52,659,296
Entity Public Float			$ 716,784,346
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	001-34628
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 Incorporation State Country Code	DE
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	587-7700
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement relating to its 2020 annual stockholders’ meeting are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated
Document Annual Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes