Fair Value of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on a Non-recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Jun. 30, 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	$ 1,029,714	$ 1,127,195
Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	21,082	6,910
Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Multi-family mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	16,385	1,896
Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Nonresidential mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	4,697	5,014
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Multi-family mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Nonresidential mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	1,029,714	1,127,195
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Multi-family mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	0	0
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Nonresidential mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	21,082
Assets, fair value	0	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable		6,910
Assets, fair value	21,082	6,910
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Multi-family mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	16,385	1,896
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Nonrecurring \| Commercial Loan \| Nonresidential mortgage
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net loans receivable	$ 4,697	$ 5,014

Kearny Financial Corp. 10-K