Business Combinations (Details) - Pacific Continental [Member] - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Nov. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 1,081	$ 1,171	$ 8,168	$ 3,558
Business Acquisition, Pro Forma Revenue					432,060
Business Combination, Consideration Transferred	$ 637,103
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2017
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Purchase Price Allocation, Goodwill Amount	$ 383,080
Business Combination, Purchase Price Allocation, Amortizable Intangible Assets	46,875
Business Combination, Purchase Price Allocation, Other Assets	50,638
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	2,554,514
Business Combination, 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, Junior Subordinated Debentures	(14,434)
Business combination, purchase price allocation, securities sold under agreements to repurchase	(1,617)
Business Combination, Purchase Price Allocation, Other Liabilities	(28,653)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	(2,300,491)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 254,023
business combinations, core deposit intangible percentage of core deposits	2.34%
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 81,190
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	449,291
Business Combination, Purchase Price Allocation, FHLB Stock	7,084
Business Combination, Acquired Receivable, Fair Value	1,873,987
Business Combination, Purchase Price Allocation, Accrued Interest Receivable	7,827
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	27,343
Business Combination, Purchase Price Allocation, Other Real Estate Owned	$ 10,279
Business Acquisition, Pro Forma Net Income (Loss)					$ 122,410
Business Acquisition, Pro Forma Earnings Per Share, Basic					$ 1.70
Business Acquisition, Pro Forma Earnings Per Share, Diluted					$ 1.70
Compensation and employee benefits [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		923	3	3,410	$ 3
Occupancy [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		29	593	1,619	945
Advertising and promotion [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		0	184	534	201
Data processing [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		20	66	941	539
Legal and professional fees [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		102	157	893	1,587
Taxes, licenses and fees [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		0	0	0	3
Other noninterest expenses [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 7	$ 168	$ 771	$ 280