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Capital Stock and Dividend Restrictions (Details) - USD ($) $ / shares in Units, $ in Millions |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Apr. 08, 2019 | Aug. 16, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Sep. 25, 2017
Class of Stock |  |  |  |  |  |
Common stock, shares authorized |  |  | 200,000,000 |  |  |
Stock compensation expense |  |  | $ 8.0 | $ 5.6 | $ 3.8 |
Aggregate purchase price of shares repurchased and retired |  |  | $ 2.5 | $ 1.0 | $ 1.3 |
Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock, shares authorized |  |  | 100,000,000 |  |  |
Common Stock, Voting Rights, Votes Per Share |  |  | $ 1 |  |  |
Common stock, shares, outstanding |  |  | 43,129,085 | 38,169,575 |  |
Common shares purchased and retired |  |  | 0 |  |  |
Class B Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock, shares authorized |  |  | 100,000,000 |  |  |
Common Stock, Voting Rights, Votes Per Share |  |  | $ 5 |  |  |
Common stock, shares, outstanding |  |  | 22,117,254 | 22,453,672 |  |
Community 1st Bank [Member] |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Total consideration paid | $ 18.8 |  |  |  |  |
Community 1st Bank [Member] | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock issued (in shares) | 463,134 |  |  |  |  |
Idaho Independent Bank [Member] |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Total consideration paid | $ 157.3 |  |  |  |  |
Class A common stock | $ 157.3 |  |  |  |  |
Idaho Independent Bank [Member] | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock issued (in shares) | 3,871,422 |  |  |  |  |
Inland Northwest Bank [Member] |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Total consideration paid |  | $ 176.3 |  |  |  |
Class A common stock |  | $ 173.3 |  |  |  |
Inland Northwest Bank [Member] | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock issued (in shares) |  | 3,840,000 |  |  |  |
Director [Member] | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Shares issued to directors during period |  |  | 22,417 |  |  |
Stock compensation expense |  |  | $ 0.8 |  |  |
Board of Directors |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Aggregate value of shares issued to directors |  |  |  | $ 0.5 |  |
Board of Directors | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Shares issued to directors during period |  |  |  | 11,389 |  |
Secondary Public Offering | Class A Common Stock |  |  |  |  |  |
Class of Stock |  |  |  |  |  |
Common stock, value authorized |  |  |  |  |  | $ 250.0

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