Dividend Availability and Regulatory Matters Dividend Availability and Regulatory Matters (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements for Mortgage Companies [Line Items]
Proceeds from Dividends Received	$ 265,000,000
Retained earnings	$ 723,471,000	$ 366,073,000
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	6.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Tier One Risk Based Capital Required to be Well Capitalized	6.50%	6.50%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Deferred Tax Assets, Regulatory Assets and Liabilities	$ 200,000
Common Equity Tier One Capital Ratio	4.50%
Supplementary Leverage Ratio	4.00%
Subordinated debentures	$ 462,437,000	$ 440,744,000
Tier One Capital, Trust Preferred Securities Capital Portion	0
Tier Two Capital, Trust Preferred Securities Capital Portion	448,800,000
Pacific Western Bank [Member]
Compliance with Regulatory Capital Requirements for Mortgage Companies [Line Items]
Retained earnings	434,800,000
Deferred Tax Assets, Regulatory Assets and Liabilities	$ 56,000

Tier One Capital, Trust Preferred Securities Capital Portion

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- Definition

Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets

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Tier Two Capital, Trust Preferred Securities Capital Portion

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- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

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Percentage of Common Equity Tier One Risk-based Capital to total risk-weighted assets, as defined by regulatory framework.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences derived regulatory assets and liabilities.

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- Definition

Dividends received on equity and other investments during the current period.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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- Definition

Percentage of tier one capital to total leverage exposure, as defined by regulatory framework.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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