Investment Securities - Narrative (Details) $ in Millions	Sep. 30, 2020 USD ($)
Investments, Debt and Equity Securities [Abstract]
AFS securities pledged as collateral	$ 605.3

Available For Sale Securities Pledged As Collateral Amortized Cost

No definition available.

Name:	pacw_AvailableForSaleSecuritiesPledgedAsCollateralAmortizedCost
Namespace Prefix:	pacw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant