Capital Stock and Dividend Restrictions (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Apr. 03, 2015
Preferred Stock
Nonvoting, noncumulative preferred stock, shares outstanding		0	0
Common Stock, Recapitalization
Common stock, shares authorized		200,000,000
Common Stock
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned				$ 35,972
Payments for Repurchase of Common Stock		$ 26,854	$ 20,647	$ 9,739
Class B Common Stock
Common Stock, Recapitalization
Common stock, shares authorized		100,000,000
Common Stock, Voting Rights		5
Common Stock
Common stock, shares, outstanding		23,312,291	23,729,631
Class A Common Stock
Class of Stock
Stock Repurchased and Retired During Period, Weighted Average Price		$ 26.16	$ 26.01
Common Stock, Recapitalization
Common stock, shares authorized		100,000,000
Common Stock, Voting Rights		1
Common Stock
Common stock, shares, outstanding		21,613,885	21,698,594
Stock Repurchased and Retired During Period, Shares		975,877	765,875
Payments for Repurchase of Common Stock		$ 25,526	$ 19,921
2015 Equity Compensation Plan [Member] | Class A Common Stock
Class of Stock
Additional Shares Authorized					2,000,000
Mountain West Bank | Class A Common Stock
Common Stock
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares				1,378,230
Board of Directors [Member]
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Aggregate Value of Shares Issued	$ 473		$ 591
Board of Directors [Member] | Class A Common Stock
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	16,347		21,414