Business Combinations (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 01, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Junior Subordinated Notes		$ 8,248	$ 0
Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Cost of Acquired Entity, Purchase Price, Total	$ 637,103
Business Combination, Acquisition Related Costs		17,196	291
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2017
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 81,190
Business Acquisition, Purchase Price Allocation, Current Assets, Marketable Securities	449,291
Business Acquisition, Purchase Price Allocation, FHLB Stock	7,084
Business Combination, Acquired Receivable, Fair Value	1,873,987
Business Acquisition, Purchase Price Allocation, Accrued Interest Receivable	7,827
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	27,343
Business Acquisition, Purchase Price Allocation, Other Real Estate Owned	10,279
Business Combination, Purchase Price Allocation, Amortizable Intangible Assets	46,875
Business Combination, Purchase Price Allocation, Other Assets	50,638
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits	(2,118,982)
Business Combination, Purchase Price Allocation, Federal Home Loan bank advances	101,127
Business Combination, Purchase Price Allocation, Subordinated Debt	(35,678)
Business combination, purchase price allocation, securities sold under agreements to repurchase	(1,617)
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	(28,653)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	254,023
Business Combination, Purchase Price Allocation, Goodwill Amount	$ 383,080
Business Acquisition, Pro Forma Revenue		571,944	520,419
Business Acquisition, Pro Forma Net Income (Loss)		$ 149,859	$ 124,550
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ 2.23	$ 1.86
Business Acquisition, Pro Forma Earnings Per Share, Diluted		$ 2.23	$ 1.86
Compensation and employee benefits [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 8,014	$ 0
Occupancy [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		1,912	0
Advertising and promotion [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		467	0
Data processing and communications [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		1,555	0
Legal and professional fees [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		4,618	291
Taxes, licenses and fees [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		10	0
Other noninterest expenses [Member] | Pacific Continental [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 620	$ 0