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