Business combinations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Nov. 01, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition [Line Items]
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	93,350
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	35,353
Business Acquisition, Purchase Price Allocation, Goodwill Amount	$ 38,585
Business Acquisition, Pro Forma Revenue					$ 197,723
Business Acquisition, Pro Forma Net Income (Loss)					$ 43,719
Business Acquisition, Pro Forma Earnings Per Share, Basic					$ 0.78
Business Acquisition, Pro Forma Earnings Per Share, Diluted					$ 0.77
Business Combination, Acquisition Related Costs		$ 5,643	$ 0	$ 8,545
business combinations, core deposit intangible percentage of core deposits	1.75%
West Coast Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs			$ 672	72	$ 1,600
Compensation and employee benefits [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		3,035		3,308
Occupancy [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		804		1,303
Advertising and promotion [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		247		343
Data processing and communications [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		180		1,738
Legal and professional fees [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		633		1,018
Other noninterest expenses [Member] | Intermountain Community Bancorp [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs		$ 744		$ 835