Regulatory Capital Matters - Additional Information (Details)	Sep. 30, 2021
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Capital conservation buffer	2.50%

Risk-weighted assets, capital conservation buffer percentage.

No definition available.

Name:	opbk_RiskWeightedAssetsCapitalConservationBufferPercentage
Namespace Prefix:	opbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant