Business Combinations (Narrative) (Details)			3 Months Ended								6 Months Ended	8 Months Ended	12 Months Ended
	Apr. 18, 2014 USD ($) $ / shares	Jul. 02, 2013 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jun. 20, 2014 USD ($) branches
Business Acquisition [Line Items]
Net earnings available to common shareholders			$ 62,923,000	$ 57,523,000	$ 54,691,000	$ 47,045,000	$ 52,436,000	$ 58,741,000	$ 17,459,000	$ 18,538,000			$ 222,182,000	$ 147,174,000	$ 97,503,000
Non-interest expense			185,911,000	183,194,000	201,918,000	192,619,000	190,856,000	182,558,000	214,131,000	96,518,000			763,642,000	684,063,000	364,661,000
Net income (loss)			63,019,000	$ 57,607,000	$ 54,784,000	$ 47,129,000	$ 52,582,000	$ 58,883,000	$ 17,542,000	$ 18,651,000			222,539,000	147,658,000	98,291,000
Merger related expenses													45,582,000	82,317,000	8,836,000
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, deposits																$ 211,500,000
Disposal group, loans receivable																$ 88,300,000
Loans	7,000,000,000
Business Combination, Acquiree, Loans, Fair Value	6,700,000,000
Business Combination, Acquiree, Discount on Loans	230,500,000
Business Combination, Pro Forma Information, Interest Income (Expense), Net Of Acquiree Since Acquisition Date, Actual												$ 339,300,000	435,500,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual												$ 64,700,000	132,000,000
Aggregate consideration to acquire entity	2,132,467,000
Cash payment paid	136,200,000
Fair value of common shares issued	$ 1,939,497,000
Merger related expenses													45,582,000	82,317,000
Sterling Financial Corporation [Member] | Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders														54,400,000	12,900,000
Sterling Financial Corporation [Member] | Equity Option [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio	1.7896
Sterling Financial Corporation [Member] | Restricted Stock Units (RSUs) [Member]
Business Acquisition [Line Items]
Equity issuable, share conversion ratio	1.7896
Financial Pacific Holding Corp [Member]
Business Acquisition [Line Items]
Tax deductible goodwill			$ 0										$ 0
Aggregate consideration to acquire entity		$ 158,000,000
Cash payment paid		156,110,000
Fair value of common shares issued		$ 1,900,000
Revenues											$ 66,100,000
Non-interest expense											15,900,000
Net income (loss)											18,700,000
Merger related expenses											$ 1,600,000			$ 110,000
Financial Pacific Holding Corp [Member] | Minimum [Member]
Business Acquisition [Line Items]
Vesting period of equity consideration		2 years
Financial Pacific Holding Corp [Member] | Maximum [Member]
Business Acquisition [Line Items]
Vesting period of equity consideration		3 years
Financial Pacific Holding Corp [Member] | Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders															$ 4,200,000