Business Combinations (Narrative) (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 18, 2014	Jul. 02, 2013	Jun. 20, 2014 branches
Business Acquisition [Line Items]
Net earnings available to common shareholders	$ 52,400,000	$ 58,847,000	$ 17,138,000	$ 18,651,000	$ 25,058,000	$ 23,281,000	$ 26,056,000	$ 23,178,000	$ 147,036,000	$ 97,573,000	$ 101,209,000
Non-interest expense	190,856,000	182,558,000	214,131,000	96,518,000	95,364,000	95,604,000	87,931,000	85,762,000	684,063,000	364,661,000	359,652,000
Net income (loss)	52,546,000	58,989,000	17,221,000	18,764,000	25,270,000	23,477,000	26,253,000	23,361,000	147,520,000	98,361,000	101,891,000
Merger related expenses									82,317,000	8,836,000	2,338,000
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								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, 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
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									82,317,000
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									110,000	1,600,000
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
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									82,400,000	12,900,000
Acquisition-related Costs [Member] | Financial Pacific Holding Corp [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders										4,200,000
Pro Forma [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders									102,476,000
Non-interest expense									373,181,000
Net income (loss)									103,305,000
Pro Forma [Member] | Sterling Financial Corporation [Member]
Business Acquisition [Line Items]
Net earnings available to common shareholders									234,831,000	204,103,000
Non-interest expense									704,488,000	802,371,000
Net income (loss)									$ 235,315,000	$ 204,891,000