Premises and Equipment, Net - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 8.2	$ 8.7	$ 6.3

Depreciation, Depletion and Amortization, Net of Purchase Accounting Accretion and Amortization

No definition available.

Name:	ocfc_DepreciationDepletionandAmortizationNetofPurchaseAccountingAccretionandAmortization
Namespace Prefix:	ocfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration