Loans Receivable and Related Allowance for Loan Losses - Schedule of modified financing receivables (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	601
Balance | $	$ 158,522
Weighted Average Interest Rate	4.60%
One-to-four-family Residential and Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	99
Balance | $	$ 19,186
Weighted Average Interest Rate	4.05%
Home Equity Loans and Lines of Credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	87
Balance | $	$ 6,059
Weighted Average Interest Rate	3.35%
Other Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	1
Balance | $	$ 10
Weighted Average Interest Rate	2.60%
Commercial Loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	414
Balance | $	$ 133,300
Commercial Loan | Commercial Real Estate and Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	369
Balance | $	$ 123,674
Weighted Average Interest Rate	4.77%
Commercial Loan | Commercial Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	45
Balance | $	$ 9,593
Weighted Average Interest Rate	4.32%
Consumer Loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified | loan	187
Balance | $	$ 25,300