Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended					0 Months Ended									1 Months Ended	0 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Aug. 01, 2012	Aug. 01, 2012	Apr. 03, 2012	Apr. 03, 2012	Apr. 07, 2014		Apr. 07, 2014		May 31, 2013	May 31, 2013	Jan. 03, 2012	Jan. 03, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Equipment leased to others under operating leases	$ 122,506		$ 0
Goodwill	1,720,479	[1]	208,743	[1]	79,866													39,141
Collection of securities sales proceeds	484,084		0		0
American Perspective Bank [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition						Aug. 01, 2012
Cash and due from banks						3,370	3,370
Interest-earning deposits in financial institutions						10,081	10,081
Investments securities available-for-sale						48,887	48,887
FHLB stock						1,412	1,412
Loans and leases						197,279	197,279
Equipment leased to others under operating leases						0	0
Premises and equipment						0	0
Foreclosed Assets						1,561	1,561
FDIC loss sharing asset						0	0
Income Tax Assets						2,194	2,194
Goodwill						15,047	15,047
Other intangible assets						1,924	1,924
Leases In Process						0	0
Other assets						2,040	2,040
Total assets acquired						283,795	283,795
Noninterest-bearing deposits						40,673	40,673
Interest-bearing deposits						178,891	178,891
Other borrowings						5,315	5,315
Borrowings from Parent						0	0
Subordinated Debentures						0	0
Discontinued operations						0	0
Accrued interest payable and other liabilities						840	840
Total liabilities assumed						225,719	225,719
Total consideration paid						58,076	58,076
Cash paid						58,076
PacWest common stock issued						0
Cancellation of FCAL common stock owned by PacWest (at acquisition date fair value)						0	0
Celtic Capital Corporation [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition								Apr. 03, 2012
Cash and due from banks								3,435	3,435
Interest-earning deposits in financial institutions								0	0
Investments securities available-for-sale								0	0
FHLB stock								0	0
Loans and leases								54,963	54,963
Equipment leased to others under operating leases								0	0
Premises and equipment								0	0
Foreclosed Assets								0	0
FDIC loss sharing asset								0	0
Income Tax Assets								19	19
Goodwill								6,645	6,645
Other intangible assets								1,300	1,300
Leases In Process								0	0
Other assets								720	720
Total assets acquired								67,082	67,082
Noninterest-bearing deposits								0	0
Interest-bearing deposits								0	0
Other borrowings								46,804	46,804
Borrowings from Parent								0	0
Subordinated Debentures								0	0
Discontinued operations								0	0
Accrued interest payable and other liabilities								2,278	2,278
Total liabilities assumed								49,082	49,082
Total consideration paid								18,000	18,000
Cash paid								18,000
PacWest common stock issued								0
Cancellation of FCAL common stock owned by PacWest (at acquisition date fair value)								0	0
Capitalsource, Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Apr. 07, 2014											Apr. 07, 2014
Cash and due from banks										768,553		768,553
Interest-earning deposits in financial institutions										60,612		60,612
Investments securities available-for-sale										382,797		382,797
FHLB stock										46,060		46,060
Loans and leases										6,877,427		6,877,427
Equipment leased to others under operating leases										160,015		160,015
Premises and equipment										12,663		12,663
Foreclosed Assets										6,382		6,382
FDIC loss sharing asset										0		0
Income Tax Assets										312,757		312,757
Goodwill										1,518,381		1,518,381
Other intangible assets										6,720		6,720
Leases In Process										0		0
Other assets										582,985	[2]	582,985	[2]
Total assets acquired										10,735,352		10,735,352
Noninterest-bearing deposits										4,631		4,631
Interest-bearing deposits										6,236,419		6,236,419
Other borrowings										992,109		992,109
Borrowings from Parent										0		0
Subordinated Debentures										300,918		300,918
Discontinued operations										0		0
Accrued interest payable and other liabilities										124,087		124,087
Total liabilities assumed										7,658,164		7,658,164
Total consideration paid										3,077,188		3,077,188
Cash paid										483,118
PacWest common stock issued										2,594,070
Cancellation of FCAL common stock owned by PacWest (at acquisition date fair value)										0		0
First California Financial Group, Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition														May 31, 2013
Cash and due from banks														6,124	6,124
Interest-earning deposits in financial institutions														266,889	266,889
Investments securities available-for-sale														4,444	4,444
FHLB stock														9,518	9,518
Loans and leases														1,049,613	1,049,613
Equipment leased to others under operating leases														0	0
Premises and equipment														15,322	15,322
Foreclosed Assets														13,772	13,772
FDIC loss sharing asset														17,241	17,241
Income Tax Assets														33,360	33,360
Goodwill														129,070	129,070
Other intangible assets														7,927	7,927
Leases In Process														0	0
Other assets														27,576	27,576
Total assets acquired														1,580,856	1,580,856
Noninterest-bearing deposits														361,166	361,166
Interest-bearing deposits														739,713	739,713
Other borrowings														0	0
Borrowings from Parent														0	0
Subordinated Debentures														24,061	24,061
Discontinued operations														184,619	184,619
Accrued interest payable and other liabilities														19,729	19,729
Total liabilities assumed														1,329,288	1,329,288
Total consideration paid														251,568	251,568
Cash paid														0
PacWest common stock issued														242,268
Cancellation of FCAL common stock owned by PacWest (at acquisition date fair value)														9,300	9,300
Pacific Western Equipment Finance [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition																Jan. 03, 2012
Cash and due from banks																7,092	7,092
Interest-earning deposits in financial institutions																0	0
Investments securities available-for-sale																0	0
FHLB stock																0	0
Loans and leases																140,959	140,959
Equipment leased to others under operating leases																0	0
Premises and equipment																0	0
Foreclosed Assets																0	0
FDIC loss sharing asset																0	0
Income Tax Assets																0	0
Goodwill																19,033	19,033
Other intangible assets																1,700	1,700
Leases In Process																19,162	19,162
Other assets																1,887	1,887
Total assets acquired																189,833	189,833
Noninterest-bearing deposits																0	0
Interest-bearing deposits																0	0
Other borrowings																15,839	15,839
Borrowings from Parent																128,677	128,677
Subordinated Debentures																0	0
Discontinued operations																0	0
Accrued interest payable and other liabilities																10,317	10,317
Total liabilities assumed																154,833	154,833
Total consideration paid																35,000	35,000
Cash paid																35,000
PacWest common stock issued																0
Cancellation of FCAL common stock owned by PacWest (at acquisition date fair value)																$ 0	$ 0

[1] (1)The increase in the goodwill for the Community Banking segment and National Lending segment during 2014 was due primarily to $1.5 billion from the CapitalSource merger.

[2] (1) The CapitalSouce, Inc. amount includes a $484 million receivable for securities sales proceeds.