Business Combinations narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 01, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Threshold for average assets requiring CFPB examination		$ 10,000,000
Estimated pre-tax annual impact of no longer qualifying for the small issuer exemption from interchange fee cap		10,000
Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Purchase Price Allocation, Junior Subordinated Debentures	$ (14,434)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	(2,300,491)
Business Combination, Purchase Price Allocation, Goodwill Amount	$ 383,080
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2017
Business Combination, Cost of Acquired Entity, Purchase Price, Total	$ 637,103
Business Combination, Acquired Receivable, Fair Value	1,873,987
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	254,023
Business Combination, Purchase Price Allocation, Amortizable Intangible Assets	$ 46,875
business combinations, core deposit intangible percentage of core deposits	2.34%
Business Combination, Acquisition Related Costs		$ 17,196	$ 291
Business Combination, Purchase Price Allocation, Other Assets	$ 50,638
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	2,554,514
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits	$ 2,118,982
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Purchase Price Allocation, Federal Home Loan bank advances	$ (101,127)