Stockholders' Equity - Summary of Bank's Regulatory Capital Levels (Details) $ in Thousands	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)
Actual Amount
Total capital (to risk-weighted assets)	$ 761,657	$ 748,323
Tier 1 capital (to risk-weighted assets)	714,716	705,586
Common equity tier 1 capital (to risk-weighted assets)	714,716	705,586
Tier 1 capital (to adjusted total assets)	$ 714,716	$ 705,586
Actual Ratio
Total capital (to risk-weighted assets)	0.1527	0.1537
Tier 1 capital (to risk-weighted assets)	0.1433	0.1449
Common equity tier 1 capital (to risk-weighted assets)	0.1433	0.1449
Tier 1 capital (to adjusted total assets)	0.0941	0.0923
For Capital Adequacy Purposes Amount
Total capital (to risk-weighted assets)	$ 398,916	$ 389,434
Tier 1 capital (to risk-weighted assets)	299,187	292,076
Common equity tier 1 capital (to risk-weighted assets)	224,390	219,057
Tier 1 capital (to adjusted total assets)	$ 303,751	$ 305,661
For Capital Adequacy Purposes Ratio
Total capital (to risk-weighted assets)	0.0800	0.0800
Tier 1 capital (to risk-weighted assets)	0.0600	0.0600
Common equity tier 1 capital (to risk-weighted assets)	0.0450	0.0450
Tier 1 capital (to adjusted total assets)	0.0400	0.0400
Kearny Federal Savings Bank
Actual Amount
Total capital (to risk-weighted assets)	$ 716,311	$ 704,969
Tier 1 capital (to risk-weighted assets)	669,370	662,232
Common equity tier 1 capital (to risk-weighted assets)	669,370	662,232
Tier 1 capital (to adjusted total assets)	$ 669,370	$ 662,232
Actual Ratio
Total capital (to risk-weighted assets)	0.1438	0.1449
Tier 1 capital (to risk-weighted assets)	0.1344	0.1361
Common equity tier 1 capital (to risk-weighted assets)	0.1344	0.1361
Tier 1 capital (to adjusted total assets)	0.0883	0.0868
For Capital Adequacy Purposes Amount
Total capital (to risk-weighted assets)	$ 398,556	$ 389,184
Tier 1 capital (to risk-weighted assets)	298,917	291,888
Common equity tier 1 capital (to risk-weighted assets)	224,188	218,916
Tier 1 capital (to adjusted total assets)	$ 303,109	$ 305,162
For Capital Adequacy Purposes Ratio
Total capital (to risk-weighted assets)	0.0800	0.0800
Tier 1 capital (to risk-weighted assets)	0.0600	0.0600
Common equity tier 1 capital (to risk-weighted assets)	0.0450	0.0450
Tier 1 capital (to adjusted total assets)	0.0400	0.0400
To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount
Total capital (to risk-weighted assets)	$ 498,196	$ 486,481
Tier 1 capital (to risk-weighted assets)	398,556	389,184
Common equity tier 1 capital (to risk-weighted assets)	323,827	316,212
Tier 1 capital (to adjusted total assets)	$ 378,886	$ 381,453
To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio
Total capital (to risk-weighted assets)	0.1000	0.1000
Tier 1 capital (to risk-weighted assets)	0.0800	0.0800
Common equity tier 1 capital (to risk-weighted assets)	0.0650	0.0650
Tier 1 capital (to adjusted total assets)	5.00%	5.00%

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