Acquisitions Business Combinations (Details) $ in Thousands			12 Months Ended
	Aug. 12, 2016 USD ($)	Jul. 24, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares
Business Acquisition [Line Items]
Acquisition Expense			$ 2,821	$ 795	$ 4,017
Goodwill, Purchase Accounting Adjustments			$ 42
Flathead Bank [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Aug. 12, 2016
Flathead Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 34,100
United Bank [Member]
Business Acquisition [Line Items]
Number of Subsidiary Banks		1
Number of Shared Markets		3
Estimate of Payments to Acquire Businesses, Gross		$ 7,234
Business Acquisition, Effective Date of Acquisition		Jul. 24, 2015
Mountain West Bank | Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares					1,378,230