Acquisitions (Details) - USD ($) $ in Thousands	Apr. 07, 2014	Sep. 30, 2015	Dec. 31, 2014
Assets Acquired:
Equipment leased to others under operating leases		$ 161,508	$ 122,506
Goodwill		$ 1,728,380	$ 1,720,479
Capitalsource, Inc. [Member]
Assets Acquired:
Cash and due from banks	$ 768,553
Interest‑earning deposits in financial institutions	60,612
Investment securities available‑for‑sale	382,797
FHLB stock	46,060
Loans and leases	6,877,427
Equipment leased to others under operating leases	160,015
Premises and equipment	12,663
Foreclosed assets	6,382
Income tax assets	304,856
Goodwill	1,526,282
Core deposit and customer relationship intangibles	6,720
Other assets	582,985
Total assets acquired	10,735,352
Liabilities Assumed:
Noninterest‑bearing deposits	4,631
Interest‑bearing deposits	6,236,419
Other borrowings	992,109
Subordinated debentures	300,918
Accrued interest payable and other liabilities	124,087
Total liabilities assumed	7,658,164
Total consideration paid	3,077,188
Cash paid	483,118
PacWest common stock issued	$ 2,594,070