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