Acquisitions Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands		Aug. 12, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					$ 35,972
Goodwill			$ 212,820	$ 204,523
Flathead Bank Acquisition, as recorded by Flathead Bank [Member]
Business Acquisition [Line Items]
Cash and Cash Equivalents		$ 52,653
Investment Securities		99,801
Loans		87,181
Allowance for Loan Losses		(1,567)
Premises and Equipment		4,529
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Company Owned LIfe Insurance		6,386
Core Deposit Intangibles		0
Other Assets		5,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		254,183
Deposits		209,673
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Securities Under Agreement to Repurchase		18,050
Other Liabilities		838
Total Liabilities Assumed		228,561
Net Assets Acquired		25,622
Flathead Bank Acquisition, Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Cash and Cash Equivalents		0
Investment Securities	[1]	1,315
Loans	[2]	(3,833)
Allowance for Loan Losses	[3]	1,567
Premises and Equipment	[4]	891
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Company Owned LIfe Insurance		0
Core Deposit Intangibles	[5]	2,486
Other Assets	[6]	(2,373)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		53
Deposits	[7]	(86)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Securities Under Agreement to Repurchase		0
Other Liabilities		0
Total Liabilities Assumed		(86)
Net Assets Acquired		139
Flathead Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Cash and Cash Equivalents		52,653
Investment Securities		101,116
Loans		83,348
Allowance for Loan Losses		0
Premises and Equipment		5,420
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Company Owned LIfe Insurance		6,386
Core Deposit Intangibles		2,486
Other Assets		2,827
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		254,236
Deposits		209,587
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Securities Under Agreement to Repurchase		18,050
Other Liabilities		838
Total Liabilities Assumed		228,475
Net Assets Acquired		25,761
Payments to Acquire Businesses, Gross		34,100
Goodwill		$ 8,339

[1] (1) Write up of the book value of investments to their estimated fair values on the date of acquisition based upon quotes obtained from an independent third party pricing service.

[2] (2) Write down of the book value of loans to their estimated fair values. The fair value of loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company's analysis of the fair value of each loan's underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral.

[3] (3) Adjustment to remove the Flathead allowance for loan losses at acquisition date as the credit risk is accounted for in the fair value adjustment for loans receivable described in (2) above.

[4] (4) Write up of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon appraisals obtained from an independent third party appraiser or pending buy/sell agreements.

[5] (5) Adjustment represents the value of the core deposit base assumed in the acquisition based upon an internal valuation using industry averages obtained from an investment banking firm.

[6] (6) Adjustment consists of the write-off of pre-existing goodwill and prepaid assets.

[7] (7) Decrease in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition.