Acquisitions - Assets Acquired and Liabilities Assumed in Roselle Acquisition (Details) - USD ($)	Apr. 01, 2020	Sep. 30, 2020
Liabilities assumed:
Goodwill		$ 0
Roselle Entities
Assets acquired:
Cash and cash equivalents	$ 155,248,000
Debt securities available for sale	51,479,000
Debt securities held to maturity	13,418,000
Equity securities	1,796,000
Federal Home Loan Bank stock	2,010,000
Loans receivable	171,593,000
Accrued interest receivable	679,000
Office properties and equipment, net	5,774,000
Bank-owned life insurance	17,245,000
Deferred tax asset, net	1,334,000
Other assets	1,489,000
Total assets acquired	422,065,000
Liabilities assumed:
Deposits	333,234,000
Borrowings	37,728,000
Advance payments by borrowers for taxes and insurance	982,000
Accrued expenses and other liabilities	5,400,000
Total liabilities assumed	377,344,000
Net assets acquired	44,721,000
Fair market value of stock issued to Columbia Bank MHC for purchase	68,530,000
Goodwill	$ 23,809,000