| Cover | Apr. 23, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 23, 2021 |
| Entity File Number | 001-36408 |
| Entity Registrant Name | PacWest Bancorp |
| Entity Central Index Key | 0001102112 |
| Entity Tax Identification Number | 33-0885320 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 9701 Wilshire Blvd. |
| Entity Address, Address Line Two | Suite 700 |
| Entity Address, City or Town | Beverly Hills |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 90212 |
| City Area Code | 310 |
| Local Phone Number | 887-8500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | PACW |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
