Acquisitions Acquisitions (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015		Apr. 07, 2014		Dec. 31, 2014	Mar. 31, 2014
Business Acquisition [Line Items]
Equipment leased to others under operating leases	$ 119,959,000				$ 122,506,000
Goodwill	1,728,380,000	[1]			1,720,479,000	208,743,000
Proceeds from Sale of Other Receivables	484,000,000
Capitalsource, Inc. [Member]
Business Acquisition [Line Items]
Cash and due from banks			768,553,000
Interest-earning deposits in financial institutions			60,612,000
Investments securities available-for-sale			382,797,000
FHLB stock			46,060,000
Loans and leases			6,877,427,000
Equipment leased to others under operating leases			160,015,000
Premises and equipment			12,663,000
Foreclosed assets			6,382,000
Income Tax Assets			304,856,000
Goodwill			1,526,282,000
Other intangible assets			6,720,000
Other assets			582,985,000	[2]
Total assets acquired			10,735,352,000
Noninterest-bearing deposits			4,631,000
Interest-bearing deposits			6,236,419,000
Other borrowings			992,109,000
Subordinated Debentures			300,918,000
Accrued interest payable and other liabilities			124,087,000
Total liabilities assumed			7,658,164,000
Total consideration paid			3,077,188,000
Cash paid			483,118,000
PacWest common stock issued			$ 2,594,070,000

[1] The increase in goodwill for the Community Banking segment and National Lending segment compared to March 31, 2014, was due primarily to $1.5 billion from the CapitalSource Inc. merger.

[2] (1) Includes a $484 million receivable for securities sales proceeds.