Acquisitions Purchase Accounting Fair Value Adjustments (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended
	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Purchase Accounting Fair Value Adjustments [Line Items]
Goodwill		$ 180,128	$ 120,164
Northwestern Bancorp [Member]
Purchase Accounting Fair Value Adjustments [Line Items]
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock	119,428
Business Combination, Consideration Transferred, Cash Paid Stock Option Cancellation Agreements	1,580
Business Combination, Consideration Transferred	(121,008)
Net Assets Acquired, Acquiree Shareholders Equity	70,081
Purchase Accounting Fair Value Adjustment, Loans	(32,500)
Purchase Accounting Fair Value Adjustment, Allowance for Loan Losses	16,453
Purchase Accounting Fair Value Adjustment, Deferred Tax Asset, Net	5,787
Purchase Accounting Fair Value Adjustment, Premises and Equipment	(8,961)
Purchase Accounting Fair Value Adjustment, Core Deposit Intangible Asset	12,891
Purchase Accounting Fair Value Adjustment, Mortgage Servicing Rights Asset	1,568
Purchase Accounting Fair Value Adjustment, Acquiree Goodwill	(2,050)
Purchase Accounting Fair Value Adjustment, Other Real Estate	(800)
Purchase Accounting Fair Value Adjustment, Reserve for Sold Loans	(1,650)
Purchase Accounting Fair Value Adjustment, Other Assets and Liabilities, Net	225
Net Assets Acquired After Purchase Accounting Fair Value Adjustments	61,044
Goodwill	$ 59,964