Capital Stock (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			6 Months Ended		9 Months Ended	12 Months Ended
	Apr. 08, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2019	Jun. 11, 2019
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value		$ 32.6	$ 2.4
Common Stock, Par or Stated Value Per Share		$ 29.56
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)		42,465,637						43,129,085
Stock Repurchased and Retired During Period, Value			$ 31.2
Shares authorized to repurchase (in shares)									2,500,000
Stock repurchased and retired (in shares)			1,054,700				0	0
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased			1,445,300
Class B Common Stock
Class of Stock [Line Items]
Shares outstanding (in shares)		22,086,944						22,117,254
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
Community 1st Bank | Class A Common Stock
Class of Stock [Line Items]
Number of shares issued as consideration (in shares)	463,134
Director [Member] | Class A Common Stock
Class of Stock [Line Items]
Common Stock, Shares, Issued		291