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Capital Stock (Details) - USD ($) $ in Millions |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 08, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Mar. 31, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Jun. 11, 2019 | Dec. 31, 2018
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Stock repurchased and retired (in shares) |  |  | 607 | 39,360 | 896 | 22,596 |  |  |  |
Class A Common Stock |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares outstanding (in shares) |  |  |  |  |  |  | 43,034,082 |  |  | 38,169,575
Remaining shares authorized to purchased (in shares) |  |  |  |  |  |  |  |  | 24,123 |
Shares authorized to repurchase (in shares) |  |  |  |  |  |  |  |  | 2,500,000 |
Shares repurchased under current authorization (in shares) |  | 0 |  |  |  |  |  |  |  |
Stock repurchased and retired (in shares) |  |  |  |  |  |  | 0 | 0 |  |
Class B Common Stock |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares outstanding (in shares) |  |  |  |  |  |  | 22,195,679 |  |  | 22,453,672
Idaho Independent Bank |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Value of common stock consideration issued | $ 157.3 |  |  |  |  |  |  |  |  |
Idaho Independent Bank | Class A Common Stock |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued as consideration (in shares) | 3,871,422 |  |  |  |  |  |  |  |  |
Value of common stock consideration issued | $ 157.3 |  |  |  |  |  |  |  |  |
Community 1st Bank | Class A Common Stock |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued as consideration (in shares) | 463,134 |  |  |  |  |  |  |  |  |
Value of common stock consideration issued | $ 18.8 |  |  |  |  |  |  |  |  |
Directors | Class A Common Stock |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares issued for annual service (in shares) |  |  |  |  |  |  | 21,942 |  |  |
Aggregate value of shares issued |  |  |  |  |  |  | $ 0.8 |  |  |

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