Organization	9 Months Ended
Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	ORGANIZATION PacWest Bancorp, a Delaware corporation, is a bank holding company registered under the BHCA, with our corporate headquarters located in Beverly Hills, California. Our principal business is to serve as the holding company for our wholly-owned subsidiary, Pacific Western Bank. References to "Pacific Western" or the "Bank" refer to Pacific Western Bank together with its wholly-owned subsidiaries. References to "we," "us," or the "Company" refer to 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. We are focused on relationship-based business banking to small, middle-market and venture-backed businesses nationwide. At September 30, 2017, the Bank offers a broad range of loan and lease and deposit products and services through 74 full-service branches located throughout the State of California, one branch located in Durham, North Carolina, and several loan production offices located in cities across the country. We provide commercial banking services, including real estate, construction, and commercial loans, and comprehensive deposit and treasury management services to small and middle-market businesses. We offer additional products and services through our CapitalSource and Square 1 Bank divisions. Our CapitalSource Division provides cash flow, asset-based, equipment, and real estate loans and treasury management services to established middle market businesses on a national basis. Our Square 1 Bank Division offers a comprehensive suite of financial services focused on entrepreneurial businesses and their venture capital and private equity investors, with offices located in key innovation hubs across the United States. In addition, we provide investment advisory and asset management services to select clients through Square 1 Asset Management, Inc., a wholly-owned subsidiary of the Bank and a SEC-registered investment adviser. 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 are compensation, occupancy, general operating expenses, and the interest paid by the Bank on deposits and borrowings. We have completed 28 acquisitions from May 1, 2000 through September 30, 2017. 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 12. Subsequent Events, for information regarding the completion of the CU Bancorp acquisition on October 20, 2017. 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, 2016 as filed with the Securities and Exchange Commission ("Form 10-K"). Accounting Standards Adopted in 2017 Effective January 1, 2017, the Company adopted ASU 2016-09, "Improvements to Employee Share-Based Accounting." ASU 2016-09 changed aspects of the accounting for share-based payment award transactions, including: (1) accounting for income taxes; (2) classification of excess tax benefits on the statement of cash flows; (3) forfeitures; (4) minimum statutory tax withholding requirements; and (5) classification of employee taxes paid on the statement of cash flows when an employer withholds shares for tax-withholding purposes. The recognition of excess tax benefits and tax deficiencies in the income statement was adopted prospectively. Income tax benefits of $0.03 million and $1.5 million were recognized during the three and nine months ended September 30, 2017 as a result of the adoption of ASU 2016-09. We expect the requirements of ASU 2016-09 to result in fluctuations in our effective tax rate from period to period based upon the timing of share-based award vestings. In connection with the adoption of ASU 2016-09, we elected to recognize forfeitures on stock-based compensation awards when they occur, instead of estimating forfeitures at the grant date of the awards and throughout the vesting period. The modified retrospective application of this change in accounting principle resulted in a cumulative adjustment charge to retained earnings of $420,000, net of income taxes. We elected to present the classification of excess tax benefits on the statement of cash flows using a prospective transition method and the prior period has not been adjusted. Effective July 1, 2017, the Company early-adopted ASU 2017-08, "Receivables - Nonrefundable Fees and Other Costs (Subtopic 210-20): Premium Amortization on Purchased Callable Debt Securities." ASU 2017-08 requires certain premiums on callable debt securities to be amortized to the earliest call date. The amortization period for discounts on callable debt securities was not impacted. The adoption of this ASU had no material impact on the Company's consolidated financial position, results of operations, or cash flows. Basis of Presentation Our interim condensed consolidated financial statements are prepared in accordance with 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 significant intercompany accounts and transactions have been eliminated and adjustments, consisting solely of normal recurring accruals and 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 condensed 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. Use of Estimates We have made a number of estimates and assumptions related 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. Actual results could differ from those estimates. Material estimates subject to change in the near term include, among other items, the allowance for credit losses, the carrying value of intangible assets, 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. Reclassifications Certain prior period amounts have been reclassified to conform to the current period’s presentation format. On the condensed consolidated statements of earnings, beginning with our June 30, 2017 results, we began presenting a new line for "Loan expense" as that category exceeded the disclosure materiality threshold, which previously had been included as part of "Other expense." Included in loan expense are costs related to servicing our loans including legal fees. Prior to 2017, time deposit disclosures were presented as: (1) under $100,000, and (2) $100,000 or more. We are now using the current FDIC insurance limit of $250,000 and presenting the categories as: (1) $250,000 and under, and (2) over $250,000.

ORGANIZATION

PacWest Bancorp, a Delaware corporation, is a bank holding company registered under the BHCA, with our corporate headquarters located in Beverly Hills, California. Our principal business is to serve as the holding company for our wholly-owned subsidiary, Pacific Western Bank. References to "Pacific Western" or the "Bank" refer to Pacific Western Bank together with its wholly-owned subsidiaries. References to "we," "us," or the "Company" refer to 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.

We are focused on relationship-based business banking to small, middle-market and venture-backed businesses nationwide. At September 30, 2017, the Bank offers a broad range of loan and lease and deposit products and services through 74 full-service branches located throughout the State of California, one branch located in Durham, North Carolina, and several loan production offices located in cities across the country. We provide commercial banking services, including real estate, construction, and commercial loans, and comprehensive deposit and treasury management services to small and middle-market businesses. We offer additional products and services through our CapitalSource and Square 1 Bank divisions. Our CapitalSource Division provides cash flow, asset-based, equipment, and real estate loans and treasury management services to established middle market businesses on a national basis. Our Square 1 Bank Division offers a comprehensive suite of financial services focused on entrepreneurial businesses and their venture capital and private equity investors, with offices located in key innovation hubs across the United States. In addition, we provide investment advisory and asset management services to select clients through Square 1 Asset Management, Inc., a wholly-owned subsidiary of the Bank and a SEC-registered investment adviser.

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 are compensation, occupancy, general operating expenses, and the interest paid by the Bank on deposits and borrowings.

We have completed 28 acquisitions from May 1, 2000 through September 30, 2017. 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 12. Subsequent Events, for information regarding the completion of the CU Bancorp acquisition on October 20, 2017.

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, 2016 as filed with the Securities and Exchange Commission ("Form 10-K").

Accounting Standards Adopted in 2017

Effective January 1, 2017, the Company adopted ASU 2016-09, "Improvements to Employee Share-Based Accounting." ASU 2016-09 changed aspects of the accounting for share-based payment award transactions, including: (1) accounting for income taxes; (2) classification of excess tax benefits on the statement of cash flows; (3) forfeitures; (4) minimum statutory tax withholding requirements; and (5) classification of employee taxes paid on the statement of cash flows when an employer withholds shares for tax-withholding purposes. The recognition of excess tax benefits and tax deficiencies in the income statement was adopted prospectively. Income tax benefits of $0.03 million and $1.5 million were recognized during the three and nine months ended September 30, 2017 as a result of the adoption of ASU 2016-09. We expect the requirements of ASU 2016-09 to result in fluctuations in our effective tax rate from period to period based upon the timing of share-based award vestings.

In connection with the adoption of ASU 2016-09, we elected to recognize forfeitures on stock-based compensation awards when they occur, instead of estimating forfeitures at the grant date of the awards and throughout the vesting period. The modified retrospective application of this change in accounting principle resulted in a cumulative adjustment charge to retained earnings of $420,000, net of income taxes. We elected to present the classification of excess tax benefits on the statement of cash flows using a prospective transition method and the prior period has not been adjusted.

Effective July 1, 2017, the Company early-adopted ASU 2017-08, "Receivables - Nonrefundable Fees and Other Costs (Subtopic 210-20): Premium Amortization on Purchased Callable Debt Securities." ASU 2017-08 requires certain premiums on callable debt securities to be amortized to the earliest call date. The amortization period for discounts on callable debt securities was not impacted. The adoption of this ASU had no material impact on the Company's consolidated financial position, results of operations, or cash flows.

Basis of Presentation

Our interim condensed consolidated financial statements are prepared in accordance with 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 significant intercompany accounts and transactions have been eliminated and adjustments, consisting solely of normal recurring accruals and 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 condensed 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.

Use of Estimates

We have made a number of estimates and assumptions related 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. Actual results could differ from those estimates. Material estimates subject to change in the near term include, among other items, the allowance for credit losses, the carrying value of intangible assets, 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.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period’s presentation format. On the condensed consolidated statements of earnings, beginning with our June 30, 2017 results, we began presenting a new line for "Loan expense" as that category exceeded the disclosure materiality threshold, which previously had been included as part of "Other expense." Included in loan expense are costs related to servicing our loans including legal fees. Prior to 2017, time deposit disclosures were presented as: (1) under $100,000, and (2) $100,000 or more. We are now using the current FDIC insurance limit of $250,000 and presenting the categories as: (1) $250,000 and under, and (2) over $250,000.