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Commitments and Contingencies (Details) $ / shares in Units, $ in Millions | Oct. 11, 2018 USD ($) $ / shares | Sep. 30, 2018 USD ($) | Aug. 16, 2018 | Dec. 31, 2017 USD ($)
--- | --- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |  |
Notional amount of terminated commitment |  | $ 464.2 |  | $ 433.0
Mortgage Loans Held for Sale |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Mortgage loans with recourse provision in effect |  | 0.5 |  |
Construction Contracts |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Commitments under construction contracts |  | $ 5.4 |  |
Inland Northwest Bank |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Number of banking offices acquired |  |  | 20 |
Subsequent Event | Idaho Independent Bank [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Number of banking offices acquired | 11 |  |  |
Estimate of Payments to Acquire Businesses, Gross | $ 181.3 |  |  |
Subsequent Event | Community 1st Bank [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Number of banking offices acquired | 3 |  |  |
Estimate of Payments to Acquire Businesses, Gross | $ 21.5 |  |  |
Community 1st Bank [Member] | Subsequent Event |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Estimate value per share of Acquisition | $ / shares | $ 17.20 |  |  |
Inland Northwest Bank | Subsequent Event |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Estimate value per share of Acquisition | $ / shares | $ 22.73 |  |  |

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