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Restricted Stock Amortization

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Vesting period of time-based restricted stock, higher limit

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Vesting period of time-based restricted stock, lower limit

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Percentage of vesting of award under share-based payment arrangement.

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Stock-Based Compensation - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Amortization \| $	$ 7,100	$ 7,300	$ 19,200	$ 19,300
Unvested restricted shares (shares)	1,706,690		1,706,690		1,513,197
Vesting period of time-based restricted stock, lower limit			three
Vesting period of time-based restricted stock, higher limit			4 years
Discount From Appraisals \| Weighted Average \| Non Purchased Credit Impaired Loans and Leases \| Level 3 \| Fair Value, Measurements, Nonrecurring \| Measurement Input, Discount Rate \| Third party appraisals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rates			0.2300
Discount From Appraisals \| Minimum \| Non Purchased Credit Impaired Loans and Leases \| Level 3 \| Fair Value, Measurements, Nonrecurring \| Measurement Input, Discount Rate \| Third party appraisals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rates			0.2300
Discount From Appraisals \| Maximum \| Non Purchased Credit Impaired Loans and Leases \| Level 3 \| Fair Value, Measurements, Nonrecurring \| Measurement Input, Discount Rate \| Third party appraisals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rates			0.2300
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted shares (shares)	315,008		315,008
Vesting term			3 years
Performance Shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			0.00%
Performance Shares, One \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			150.00%
Performance Shares, Two \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			200.00%
PacWest 2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (shares)	4,000,000		4,000,000
Number of shares available for grant (shares)	1,670,705		1,670,705
Unrecognized share based compensation expense \| $	$ 50,600		$ 50,600
PacWest 2017 Stock Incentive Plan [Member] \| Time-Based Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted shares (shares)	1,706,690		1,706,690