Business combinations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Nov. 01, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition [Line Items]
Business combinations, provisional information, initial accounting incomplete, adjustment, other assets	$ 225
Business combinations, provisional information, initial accounting incomplete, adjustment, goodwill	$ 225
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2014
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 131,935
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	47,283
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	299,458
Business Combination, Purchase Price Allocation, FHLB Stock	2,124
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	93,125
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits	(736,795)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	(22,904)
Business combination, purchase price allocation, securities sold under agreements to repurchase	(59,043)
Business Combination, Purchase Price Allocation, Other Liabilities	(13,725)
Business Combination, Acquired Receivables, Fair Value	502,595
Business Combination, Purchase Price Allocation, Accrued Interest Receivable	4,656
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	20,696
Business Combination, Purchase Price Allocation, Other Real Estate Owned	2,752
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets	10,900
Business Combination, Purchase Price Allocation, Other Assets	35,128
Business Acquisition, Purchase Price Allocation, Goodwill Amount	$ 38,810
Business Acquisition, Pro Forma Revenue					$ 300,151
Business Acquisition, Pro Forma Net Income (Loss)					$ 66,788
Business Acquisition, Pro Forma Earnings Per Share, Basic					$ 1.19
Business Acquisition, Pro Forma Earnings Per Share, Diluted					$ 1.18
Business Combination, Acquisition Related Costs		$ 428	$ 459	$ 8,973	$ 459
business combinations, core deposit intangible percentage of core deposits	1.75%
West Coast Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs			2,800	72	4,400
Compensation and employee benefits [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		0	0	3,308	0
Occupancy [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		181	0	1,484	0
Advertising and promotion [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		40	27	383	27
Data processing and communications [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		42	0	1,780	0
Legal and professional fees [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		71	388	1,089	388
Other noninterest expenses [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 94	$ 44	$ 929	$ 44