Stockholders' Equity - Summary of Bank's Regulatory Capital Levels (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Jun. 30, 2021
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 778,253	$ 872,823
Tier 1 capital (to risk-weighted assets), Actual, Amount	748,315	837,677
Core (Tier 1) capital (to adjusted total assets), Actual, Amount	748,315	837,677
Tangible capital (to adjusted total assets), Actual, Amount	$ 748,315	$ 837,677
Total capital (to risk-weighted assets), Actual, Ratio	15.17%	19.65%
Tier 1 capital (to risk-weighted assets), Actual, Ratio	14.58%	18.86%
Core (Tier 1) capital (to adjusted total assets), Actual, Ratio	14.58%	18.86%
Tangible capital (to adjusted total assets), Actual, Ratio	10.14%	11.76%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 410,515	$ 355,274
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	307,886	266,456
Core (Tier 1) capital (to adjusted total assets), For Capital Adequacy Purposes, Amount	230,914	199,842
Tangible capital (to adjusted total assets), For Capital Adequacy Purposes, Amount	$ 295,290	$ 284,877
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Core (Tier 1) capital (to adjusted total assets), For Capital Adequacy Purposes, Ratio	4.50%	4.50%
Tangible capital (to adjusted total assets), For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Kearny Federal Savings Bank [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 672,274	$ 761,883
Tier 1 capital (to risk-weighted assets), Actual, Amount	642,336	726,737
Core (Tier 1) capital (to adjusted total assets), Actual, Amount	642,336	726,737
Tangible capital (to adjusted total assets), Actual, Amount	$ 642,336	$ 726,737
Total capital (to risk-weighted assets), Actual, Ratio	13.10%	17.22%
Tier 1 capital (to risk-weighted assets), Actual, Ratio	12.52%	16.42%
Core (Tier 1) capital (to adjusted total assets), Actual, Ratio	12.52%	16.42%
Tangible capital (to adjusted total assets), Actual, Ratio	8.70%	10.23%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	$ 410,429	$ 353,970
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Amount	307,822	265,477
Core (Tier 1) capital (to adjusted total assets), For Capital Adequacy Purposes, Amount	230,866	199,108
Tangible capital (to adjusted total assets), For Capital Adequacy Purposes, Amount	$ 295,163	$ 284,114
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Core (Tier 1) capital (to adjusted total assets), For Capital Adequacy Purposes, Ratio	4.50%	4.50%
Tangible capital (to adjusted total assets), For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Total capital (to risk-weighted assets), To be Well Capitalized under Prompt Corrective Action Provisions, Amount	$ 513,036	$ 442,462
Tier 1 capital (to risk-weighted assets), To be Well Capitalized under Prompt Corrective Action Provisions, Amount	410,429	353,970
Core (Tier 1) capital (to adjusted total assets), To be Well Capitalized under Prompt Corrective Action Provisions, Amount	333,473	287,600
Tangible capital (to adjusted total assets), To be Well Capitalized under Prompt Corrective Action Provisions, Amount	$ 368,954	$ 355,142
Total capital (to risk-weighted assets), To be Well Capitalized under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital (to risk-weighted assets), To be Well Capitalized under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Core (Tier 1) capital (to adjusted total assets), To be Well Capitalized under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Tangible capital (to adjusted total assets), To be Well Capitalized under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%