Business Combinations (Narrative) (Details)		3 Months Ended		6 Months Ended
	Apr. 18, 2014 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 20, 2014 USD ($) branches
Business Acquisition [Line Items]
Net earnings available to common shareholders		$ 54,691,000	$ 17,459,000	$ 101,736,000	$ 35,997,000
Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio	1.671
Cash conversion, per share | $ / shares	$ 2.18
Tax deductible goodwill		0		0
Securities sold under agreements to repurchase expected to be repaid	$ 500,000,000
Number of branches expected to be divested to Banner Bank | branches						6
Disposal Group, Including Discontinued Operation, Deposits						$ 211,500,000
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net						88,300,000
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Discount (Premium)						$ 7,000,000
Loans	7,000,000,000
Business Combination, Acquiree, Loans, Fair Value	6,700,000,000
Business Combination, Acquiree, Discount on Loans	$ 230,500,000
Net interest income		107,300,000		221,300,000
Net income		$ 29,100,000		$ 63,000,000
Equity Option [Member] | Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio	1.7896
Restricted Stock Units (RSUs) [Member] | Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio	1.7896
Acquisition-related Costs [Member] | Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders			$ 32,600,000		$ 48,800,000