| Document and Entity Information | Oct. 29, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 29, 2020 |
| Entity Registrant Name | KEARNY FINANCIAL CORP. |
| Entity Central Index Key | 0001617242 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-37399 |
| Entity Incorporation State Country Code | MD |
| Entity Tax Identification Number | 30-0870244 |
| Entity Address, Address Line One | 120 Passaic Avenue |
| Entity Address, City or Town | Fairfield |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07004 |
| City Area Code | (973) |
| Local Phone Number | 244-4500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | KRNY |
| Security Exchange Name | NASDAQ |
