Business Combinations (Narrative) (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 18, 2014	Jun. 20, 2014 branches
Business Acquisition [Line Items]
Net earnings available to common shareholders	$ 47,045,000	$ 18,538,000
Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio			1.671
Cash conversion, per share			$ 2.18
Tax deductible goodwill	0
Securities sold under agreements to repurchase expected to be repaid			500,000,000
Number of branches expected to be divested to Banner Bank				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	114,000,000
Net income	33,900,000
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		$ 16,100,000