Business combinations (Details) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
	Apr. 02, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Acquisition, Pro Forma Net Income (Loss)					$ 43,256,000
West Coast Bancorp [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Apr. 01, 2013
Business Acquisition, Cost of Acquired Entity, Purchase Price	540,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	312,400,000
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits	(1,880,000,000)
Business Combination, Acquired Receivables, Fair Value	1,410,000,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets	15,300,000
Business Acquisition, Purchase Price Allocation, Goodwill Amount	228,400,000
Business Acquisition, Pro Forma Revenue					177,970,000
Business Acquisition, Pro Forma Earnings Per Share, Basic					$ 0.85
Business Acquisition, Pro Forma Earnings Per Share, Diluted					$ 0.83
Business Combination, Acquisition Related Costs		$ 672,000	$ 9,200,000	$ 1,600,000	$ 10,000,000