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Subsequent Events (Details) $ / shares in Units, $ in Millions |  | 3 Months Ended
--- | --- | ---
Apr. 25, 2018 USD ($) office $ / shares | Mar. 31, 2018
Class A Common Stock |  |
Subsequent Event [Line Items] |  |
Declaration date of quarterly dividend |  | Apr. 25, 2018
Dividend payment date |  | May 24, 2018
Dividend record date |  | May 14, 2018
Class A Common Stock | Subsequent Event |  |
Subsequent Event [Line Items] |  |
Dividend amount per share (in dollars) | $ 0.28 |
Inland Northwest Bank [Member] | Subsequent Event |  |
Subsequent Event [Line Items] |  |
Business Acquisition, Date of Acquisition Agreement | Apr. 25, 2018 |
Number of banking offices acquired | office | 20 |
Estimate of Payments to Acquire Businesses, Gross | $ | $ 160.9 |
Estimate value per share of Acquisition | $ 21.03 |

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