Loans Receivable and Allowance for Credit Losses - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) loan segment	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($) loan	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-sale	$ 0		$ 0			$ 0
Gain on sale of loans held-for-sale	454,000	$ 63,000	1,400,000	$ 173,000
Loss on sale of loans held-for-sale	58,000	64,000	383,000	64,000
Purchases of loans receivable	0	0	14,729,000	0
Financing receivable, excluding accrued interest, before allowance for credit loss	7,840,540,000		7,840,540,000			7,677,564,000
Carrying value of servicing liability	$ 555,300,000		$ 555,300,000			$ 497,100,000
Threshold period, past due status of financial receivables			30 days
Threshold period, past due for nonperforming status of financial receivables	90 days		90 days			90 days
Non-accrual	$ 15,200,000		$ 15,200,000			$ 6,700,000
Financing receivable, excluding accrued interest, 90 days or more past due, still accruing	0		0			0
Real estate owned	0		$ 0			0
Number of loan portfolio segments | segment			7
Accrued interest receivable on loans receivable	31,600,000		$ 31,600,000			29,400,000
Specific allowance for loan losses attributable to impaired loans	631,000		631,000			339,000
Impaired loans for which there are no related allowance for loan losses	21,462,000		21,462,000			16,557,000
Off-balance sheet, credit loss, liability	5,810,000	6,611,000	5,810,000	6,611,000	$ 6,330,000	6,970,000	$ 8,358,000	$ 524,000
Off-balance sheet, credit loss, liability, credit loss expense (reversal)	(520,000)	(1,747,000)	(1,160,000)	(1,587,000)
Less Than 90 Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual	$ 2,800,000		$ 2,800,000			$ 1,200,000
Financial receivable, number of loans in nonaccrual status | loan	13		13			7
Stewardship Financial Corporation | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, excluding accrued interest, before allowance for credit loss	$ 1,700,000		$ 1,700,000			$ 2,000,000
Roselle Entities | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, excluding accrued interest, before allowance for credit loss	0		0			184,000
Freehold Entities | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, excluding accrued interest, before allowance for credit loss	2,800,000		2,800,000			3,700,000
RSI Entites | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, excluding accrued interest, before allowance for credit loss	10,700,000		10,700,000			11,300,000
Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans held-for-sale		685,000
Real estate loans | One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans held-for-sale	$ 6,800,000	1,800,000	$ 64,600,000	2,400,000
Mortgage loans in process of foreclosure, number of loans | loan	1		1
Mortgage loans in process of foreclosure, amount	$ 579,000		$ 579,000
Specific allowance for loan losses attributable to impaired loans	186,000		186,000			201,000
Impaired loans for which there are no related allowance for loan losses	1,345,000		1,345,000			1,296,000
Real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans held-for-sale			21,400,000
Specific allowance for loan losses attributable to impaired loans	307,000		307,000			99,000
Impaired loans for which there are no related allowance for loan losses	14,097,000		14,097,000			14,836,000
Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans held-for-sale	1,900,000	$ 510,000	5,700,000	1,800,000
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans held-for-sale	7,100,000		18,400,000	$ 2,000,000
Specific allowance for loan losses attributable to impaired loans	107,000		107,000			10,000
Impaired loans for which there are no related allowance for loan losses	5,819,000		5,819,000			143,000
Commercial business loans | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, excluding accrued interest, before allowance for credit loss	902,000		902,000			1,600,000
Financing receivable, unamortized loan fee	$ 0		$ 0			$ (13,000)
Consumer loans | Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans in process of foreclosure, number of loans | loan	1		1			2
Mortgage loans in process of foreclosure, amount	$ 89,000		$ 89,000			$ 81,000
Specific allowance for loan losses attributable to impaired loans	29,000		29,000			26,000
Impaired loans for which there are no related allowance for loan losses	$ 150,000		$ 150,000			$ 223,000