Business combinations (Details) (USD $)	3 Months Ended	9 Months Ended			0 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Apr. 02, 2013	Apr. 02, 2013 West Coast Bancorp [Member]	Sep. 30, 2013 West Coast Bancorp [Member]	Sep. 30, 2012 West Coast Bancorp [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue						$ 252,392,000	$ 322,941,000
Business Acquisition, Effective Date of Acquisition					Apr. 01, 2013
business combination, provisional information, initial accounting incomplete, adjustment, other liabilities	1,800,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles	622,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles	1,100,000
Business Acquisition, Cost of Acquired Entity, Purchase Price					540,791,000
Business Acquisition, Purchase Price Allocation, Current Assets, Cash and Cash Equivalents					110,440,000
Business Acquisition, Purchase Price Allocation, Current Assets, Marketable Securities					730,842,000
Business Acquisition, Purchase Price Allocation, FHLB Stock					11,824,000
Business Combination, Acquired Receivables, Fair Value					1,407,798,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment					35,884,000
Business Acquisition, Purchase Price Allocation, Loans Covered By Loss Sharing					14,708,000
Business Acquisition, Percentage of Voting Interests Acquired				100.00%
Business Acquisition, Purchase Price Allocation, Goodwill Amount					229,677,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets					15,257,000
Core deposit intangible acquired - percentage of core deposits acquired				0.89%
Business Acquisition, Purchase Price Allocation, Other Assets					76,088,000
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits					(1,883,407,000)
Business Acquisition, Purchase Price Allocation, Federal Home Loan Bank Advances					(128,885,000)
Business Acquisition, Purchase Price Allocation, Junior Subordinated Debentures					(51,000,000)
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities					(28,435,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					311,114,000
Business Acquisition, Pro Forma Net Income (Loss)		53,053,000	67,162,000
Business Acquisition, Pro Forma Earnings Per Share, Basic						$ 1.04	$ 1.29
Business Acquisition, Pro Forma Earnings Per Share, Diluted						$ 1.01	$ 1.29
Business Combination, Acquisition Related Costs						$ 17,600,000