| Document And Entity Information | Oct. 19, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 19, 2020 |
| Entity File Number | 001-34628 |
| Entity Registrant Name | QUINSTREET, INC. |
| Entity Central Index Key | 0001117297 |
| Entity Tax Identification Number | 77-0512121 |
| Entity Incorporation State Country Code | DE |
| Entity Address Address Line1 | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | QNST |
| Security Exchange Name | NASDAQ |
