Organization	3 Months Ended
Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Note 1. Organization PacWest Bancorp is a bank holding company registered under the Bank Holding Company Act of 1956, as amended. Our principal business is to serve as the holding company for our Los Angeles‑based wholly owned banking subsidiary, Pacific Western Bank, which we refer to as “Pacific Western” or the “Bank.” When we say “we,” “our,” or the “Company,” we mean PacWest Bancorp together with its subsidiaries on a consolidated basis. When we refer to “PacWest” or to the holding company, we are referring to PacWest Bancorp, the parent company, on a stand‑alone basis. As of March 31, 2015, we had total assets of $16.6 billion, gross loans and leases of $12.3 billion, total deposits of $11.9 billion and total stockholders' equity of $3.5 billion. Pacific Western is a full-service commercial bank offering a broad range of banking products and services including accepting demand, money market, and time deposits and originating loans and leases, including an array of commercial real estate loans and commercial lending products. The Bank strives to attract locally generated and relationship-based deposits, with 80 full-service branches located primarily in Southern California, extending from San Diego County to California’s Central Coast. The Bank also operates three banking offices in the San Francisco Bay area and four banking offices in the Central Valley. Our targeted collateral for real estate loan offerings includes healthcare properties, office properties, industrial properties, multifamily properties, hospitality properties, and retail properties. Our commercial loan products include equipment loans and leases, asset-based loans, loans to finance companies, and loans secured by borrower future cash flows. As a result of the CapitalSource Inc. merger, Pacific Western Bank established the CapitalSource Division, which we also refer to as the National Lending segment. The CapitalSource Division lends throughout the United States, providing middle-market businesses asset-secured loans, equipment-secured loans and leases, and cash flow loans and providing real estate loans secured by various property types. The Bank's leasing operation, Pacific Western Equipment Finance, and its group specializing in asset-based lending, CapitalSource Business Finance Group (formerly BFI Business Finance and First Community Financial), are part of the CapitalSource Division. The CapitalSource Division’s loan and lease origination efforts are conducted through offices located in Chevy Chase, Maryland; Los Angeles and San Jose, California; St. Louis, Missouri; Denver, Colorado; Chicago, Illinois; New York, New York; and Midvale, Utah. When we refer to "CapitalSource Inc." we are referring to the company acquired on April 7, 2014 and when we refer to the "CapitalSource Division" we are referring to a division of the Bank that specializes in middle-market lending on a nationwide basis. We generate our revenue primarily from interest received on loans and leases and, to a lesser extent, from interest received on investment securities, and fees received in connection with deposit services, extending credit and other services offered, including foreign exchange services. Our major operating expenses include interest paid by the Bank on deposits and borrowings, compensation and general operating expenses. We have completed 27 acquisitions from May 2000 through March 31, 2015, including the acquisition of CapitalSource Inc. Since 2000, our acquisitions have been accounted for using the acquisition method of accounting and, accordingly, the operating results of the acquired entities have been included in the consolidated financial statements from their respective acquisition dates. See Note 3, Acquisitions, for more information about the CapitalSource Inc. merger. Square 1 Financial, Inc. Merger Announcement On March 2, 2015, PacWest announced the signing of an agreement and plan of merger (the “Agreement”) whereby PacWest and Square 1 Financial, Inc. (“Square 1”) will merge in a transaction valued at approximately $849 million. The surviving company will be PacWest Bancorp and the surviving subsidiary bank will be Pacific Western Bank. The Square 1 lending operations will continue to do business under the name Square 1 as a division of Pacific Western Bank. Under the terms of the Agreement, Square 1 stockholders will receive 0.5997 shares of PacWest common stock for each share of Square 1 common stock. The total value of the per share merger consideration is $27.49, based on the $45.84 closing price of PacWest common stock on February 27, 2015, the last trading day before the transaction was announced. As of December 31, 2014, on a pro forma consolidated basis, after giving effect to the Square 1 merger, the Company would have had approximately $19.8 billion in assets with 80 branches throughout California and one branch in North Carolina. The transaction, currently expected to close in the fourth quarter of 2015, is subject to customary conditions, including the approval of bank regulatory authorities and the Square 1 stockholders. Significant Accounting Policies Except as discussed below, our accounting policies are described in Note 1, Nature of Operations and Summary of Significant Accounting Policies, of our audited consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2014 as filed with the Securities and Exchange Commission ("Form 10-K"). Accounting Standard Adopted in 2015 Effective January 1, 2015, the Company adopted new accounting guidance for investments in affordable housing projects that qualify for the low-income housing tax credit. As a result of the adoption of this new guidance, the Company made an accounting policy election to amortize the initial cost of its qualifying investments in proportion to the tax credits and other benefits received and to present the amortization as a component of income tax expense, referred to as the proportional amortization method. Previously, investments in low-income housing tax credits were accounted for under the equity method and such amortization was presented in other expense. The guidance was required to be applied retrospectively and accordingly, prior period amounts for other expense and tax expense have been revised to conform with the current period presentation. The revised amortization amounts for prior periods were not material. The retrospective application of the adoption of the new accounting guidance for the proportional amortization method resulted in a cumulative effect on retained earnings of a reduction of $195,000. Basis of Presentation Our interim consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to the requirements for reporting on Form 10-Q and Article 10 of Regulation S-X of the Securities Exchange Act of 1934. Accordingly, certain disclosures accompanying annual consolidated financial statements are omitted. In the opinion of management, all adjustments and eliminations, consisting solely of normal recurring accruals, considered necessary for the fair presentation of financial statements for the interim periods, have been included. The current period's results of operations are not necessarily indicative of the results that ultimately may be achieved for the year. The interim consolidated financial statements and notes thereto should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Form 10-K. The accompanying financial statements reflect our consolidated accounts. All significant intercompany accounts and transactions have been eliminated. Use of Estimates We have made a number of estimates and assumptions relating to the reporting of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period to prepare these condensed consolidated financial statements in conformity with U.S. GAAP. Material estimates subject to change in the near term include, among other items, the allowance for credit losses, the carrying value and useful lives of intangible assets, the carrying value of the FDIC loss sharing asset, the realization of deferred tax assets, and the fair value estimates of assets acquired and liabilities assumed in acquisitions. These estimates may be adjusted as more current information becomes available, and any adjustment may be significant. As described in Note 3, Acquisitions, the acquired assets and liabilities of CapitalSource Inc. were measured at their estimated fair values. We made significant estimates and exercised significant judgment in estimating fair values and accounting for such acquired assets and assumed liabilities. Reclassifications Certain prior period amounts have been reclassified to conform to the current period's presentation format. On the statements of earnings, the "Other expense" category includes loan-related legal expenses which were previously reported within the "Other professional services" category. On the balance sheets, the "Other assets" category includes "FDIC loss sharing asset," which was previously reported as a separate category. These reclassifications did not affect previously reported net earnings.

Note 1. Organization

PacWest Bancorp is a bank holding company registered under the Bank Holding Company Act of 1956, as amended. Our principal business is to serve as the holding company for our Los Angeles‑based wholly owned banking subsidiary, Pacific Western Bank, which we refer to as “Pacific Western” or the “Bank.” When we say “we,” “our,” or the “Company,” we mean PacWest Bancorp together with its subsidiaries on a consolidated basis. When we refer to “PacWest” or to the holding company, we are referring to PacWest Bancorp, the parent company, on a stand‑alone basis. As of March 31, 2015, we had total assets of $16.6 billion, gross loans and leases of $12.3 billion, total deposits of $11.9 billion and total stockholders' equity of $3.5 billion.

Pacific Western is a full-service commercial bank offering a broad range of banking products and services including accepting demand, money market, and time deposits and originating loans and leases, including an array of commercial real estate loans and commercial lending products. The Bank strives to attract locally generated and relationship-based deposits, with 80 full-service branches located primarily in Southern California, extending from San Diego County to California’s Central Coast. The Bank also operates three banking offices in the San Francisco Bay area and four banking offices in the Central Valley. Our targeted collateral for real estate loan offerings includes healthcare properties, office properties, industrial properties, multifamily properties, hospitality properties, and retail properties. Our commercial loan products include equipment loans and leases, asset-based loans, loans to finance companies, and loans secured by borrower future cash flows.

As a result of the CapitalSource Inc. merger, Pacific Western Bank established the CapitalSource Division, which we also refer to as the National Lending segment. The CapitalSource Division lends throughout the United States, providing middle-market businesses asset-secured loans, equipment-secured loans and leases, and cash flow loans and providing real estate loans secured by various property types. The Bank's leasing operation, Pacific Western Equipment Finance, and its group specializing in asset-based lending, CapitalSource Business Finance Group (formerly BFI Business Finance and First Community Financial), are part of the CapitalSource Division. The CapitalSource Division’s loan and lease origination efforts are conducted through offices located in Chevy Chase, Maryland; Los Angeles and San Jose, California; St. Louis, Missouri; Denver, Colorado; Chicago, Illinois; New York, New York; and Midvale, Utah. When we refer to "CapitalSource Inc." we are referring to the company acquired on April 7, 2014 and when we refer to the "CapitalSource Division" we are referring to a division of the Bank that specializes in middle-market lending on a nationwide basis.

We generate our revenue primarily from interest received on loans and leases and, to a lesser extent, from interest received on investment securities, and fees received in connection with deposit services, extending credit and other services offered, including foreign exchange services. Our major operating expenses include interest paid by the Bank on deposits and borrowings, compensation and general operating expenses.

We have completed 27 acquisitions from May 2000 through March 31, 2015, including the acquisition of CapitalSource Inc. Since 2000, our acquisitions have been accounted for using the acquisition method of accounting and, accordingly, the operating results of the acquired entities have been included in the consolidated financial statements from their respective acquisition dates. See Note 3, Acquisitions, for more information about the CapitalSource Inc. merger.

Square 1 Financial, Inc. Merger Announcement

On March 2, 2015, PacWest announced the signing of an agreement and plan of merger (the “Agreement”) whereby PacWest and Square 1 Financial, Inc. (“Square 1”) will merge in a transaction valued at approximately $849 million. The surviving company will be PacWest Bancorp and the surviving subsidiary bank will be Pacific Western Bank. The Square 1 lending operations will continue to do business under the name Square 1 as a division of Pacific Western Bank.

Under the terms of the Agreement, Square 1 stockholders will receive 0.5997 shares of PacWest common stock for each share of Square 1 common stock. The total value of the per share merger consideration is $27.49, based on the $45.84 closing price of PacWest common stock on February 27, 2015, the last trading day before the transaction was announced.

As of December 31, 2014, on a pro forma consolidated basis, after giving effect to the Square 1 merger, the Company would have had approximately $19.8 billion in assets with 80 branches throughout California and one branch in North Carolina.

The transaction, currently expected to close in the fourth quarter of 2015, is subject to customary conditions, including the approval of bank regulatory authorities and the Square 1 stockholders.

Significant Accounting Policies

Except as discussed below, our accounting policies are described in Note 1, Nature of Operations and Summary of Significant Accounting Policies, of our audited consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2014 as filed with the Securities and Exchange Commission ("Form 10-K").

Accounting Standard Adopted in 2015

Effective January 1, 2015, the Company adopted new accounting guidance for investments in affordable housing projects that qualify for the low-income housing tax credit. As a result of the adoption of this new guidance, the Company made an accounting policy election to amortize the initial cost of its qualifying investments in proportion to the tax credits and other benefits received and to present the amortization as a component of income tax expense, referred to as the proportional amortization method. Previously, investments in low-income housing tax credits were accounted for under the equity method and such amortization was presented in other expense. The guidance was required to be applied retrospectively and accordingly, prior period amounts for other expense and tax expense have been revised to conform with the current period presentation. The revised amortization amounts for prior periods were not material.

The retrospective application of the adoption of the new accounting guidance for the proportional amortization method resulted in a cumulative effect on retained earnings of a reduction of $195,000.

Basis of Presentation

Our interim consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to the requirements for reporting on Form 10-Q and Article 10 of Regulation S-X of the Securities Exchange Act of 1934. Accordingly, certain disclosures accompanying annual consolidated financial statements are omitted. In the opinion of management, all adjustments and eliminations, consisting solely of normal recurring accruals, considered necessary for the fair presentation of financial statements for the interim periods, have been included. The current period's results of operations are not necessarily indicative of the results that ultimately may be achieved for the year. The interim consolidated financial statements and notes thereto should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Form 10-K.

The accompanying financial statements reflect our consolidated accounts. All significant intercompany accounts and transactions have been eliminated.

Use of Estimates

We have made a number of estimates and assumptions relating to the reporting of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period to prepare these condensed consolidated financial statements in conformity with U.S. GAAP. Material estimates subject to change in the near term include, among other items, the allowance for credit losses, the carrying value and useful lives of intangible assets, the carrying value of the FDIC loss sharing asset, the realization of deferred tax assets, and the fair value estimates of assets acquired and liabilities assumed in acquisitions. These estimates may be adjusted as more current information becomes available, and any adjustment may be significant.

As described in Note 3, Acquisitions, the acquired assets and liabilities of CapitalSource Inc. were measured at their estimated fair values. We made significant estimates and exercised significant judgment in estimating fair values and accounting for such acquired assets and assumed liabilities.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period's presentation format. On the statements of earnings, the "Other expense" category includes loan-related legal expenses which were previously reported within the "Other professional services" category. On the balance sheets, the "Other assets" category includes "FDIC loss sharing asset," which was previously reported as a separate category. These reclassifications did not affect previously reported net earnings.