Organization (Details)		9 Months Ended
	Oct. 06, 2015 USD ($)	Sep. 30, 2015 USD ($) bank_branch acquisition	Dec. 31, 2014 USD ($)
General Introduction [Abstract]
Assets		$ 16,814,105,000	$ 16,234,605,000
Gross loans and leases		12,493,397,000	11,904,684,000
Total deposits		12,115,763,000	11,755,128,000
Total stockholders' equity		$ 3,581,704,000	3,506,230,000
Number of businesses acquired | acquisition		27
Start of acquisition activities		May 01, 2000
Retained Earnings [Member]
General Introduction [Abstract]
Total stockholders' equity		$ (57,934,000)	(285,712,000)
Other Organization Information [Abstract]
Cumulative effect of prospective application of new accounting principle			$ (195,000)
CapitalSource Inc. [Member] [Member]
General Introduction [Abstract]
Business Acquisition, Effective Date of Acquisition		Apr. 07, 2014
Square 1 Financial, Inc. [Member]
General Introduction [Abstract]
Assets		$ 21,000,000,000
Retail Branch Locations | bank_branch		80
Subsequent Event [Member]
General Introduction [Abstract]
Assets	$ 4,000,000,000
Subsequent Event [Member] | Square 1 Financial, Inc. [Member]
General Introduction [Abstract]
Business Acquisition, Effective Date of Acquisition	Oct. 06, 2015