Organization (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($) bank_branch $ / shares shares	Dec. 31, 2014 USD ($) $ / shares
General Introduction [Abstract]
Total assets	$ 16,697,020	$ 16,234,605
Gross loans and leases	12,069,005	11,904,684
Total deposits	12,581,816	11,755,128
Total stockholders' equity	$ 3,551,490	$ 3,506,230
Number of branches | bank_branch	80
Effective acquisition date	Apr. 07, 2014
Number of businesses acquired	27
Start of acquisition activities	May 01, 2000
Square 1 Financial, Inc. Acquisition Plan [Abstract]
Common Stock par value (usd per share) | $ / shares	$ 0.01	$ 0.01
Square 1 Financial, Inc. [Member]
General Introduction [Abstract]
Total assets	$ 21,100,000
Square 1 Financial, Inc. Acquisition Plan [Abstract]
Date of acquisition agreement	Mar. 02, 2015
Shares receivable by stockholders of acquiree ratio | shares	0.5997
Share price (usd per share) | $ / shares	$ 27.49
Common Stock par value (usd per share) | $ / shares	$ 45.84
Consideration valuation date
Number of Branches Upon Acquisition | bank_branch	80
Retained Earnings [Member]
General Introduction [Abstract]
Total stockholders' equity	$ (127,550)	$ (285,712)
Other Organization Information [Abstract]
Cumulative effect of prospective application of new accounting principle		$ (195)