Acquisitions (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended								12 Months Ended
	Oct. 20, 2017	Oct. 06, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Common Stock, Par or Stated Value Per Share			$ 0.01				$ 0.01				$ 0.01	$ 0.01
Goodwill			$ 2,548,670				$ 2,173,949				$ 2,548,670	$ 2,173,949	$ 2,176,291	$ 1,720,479
Acquisition, integration and reorganization costs			$ 127,258	$ 114,901	$ 116,164	$ 115,901	$ 115,929	$ 110,958	$ 110,084	$ 111,049	$ 19,735	$ 200	$ 21,247
Business Acquisition, Percentage of Voting Interests Acquired	7.00%
CU Bancorp [Member]
Business Acquisition [Line Items]
Business Acquisition Shares Receivable By Stockholders Of Acquiree Ratio	0.5308
Business Acquisition, Share Price	$ 12
Cash paid	$ 224,338
Common Stock, Par or Stated Value Per Share	$ 47.99
Assets acquired	$ 3,458,128
Liabilities assumed	2,787,557
Goodwill	374,721
Business Combination, Consideration Transferred	670,571
Loans and leases	2,075,890
Square 1 Financial, Inc. [Member]
Business Acquisition [Line Items]
Cash paid		$ 0
Assets acquired		4,611,160
Liabilities assumed		3,813,727
Goodwill		446,069
Business Combination, Consideration Transferred		797,433
Loans and leases		$ 1,553,720
Common Stock [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions											9,298,451		18,135,845
Core Deposits [Member] | CU Bancorp [Member]
Business Acquisition [Line Items]
Loans and leases	$ 2,700,000