Acquisitions Business Combinations (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			3 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Jul. 31, 2014	Feb. 10, 2014
Business Acquisition [Line Items]
Acquisition Expense	$ 4,017	$ 0	$ 0
Mountain West Bank
Business Acquisition [Line Items]
Number of Subsidiary Banks				1
Number of Shared Markets				5
Mountain West Bank
Business Acquisition [Line Items]
Business Acquisition Conversion Rate						$ 7.125
Payments to Acquire Businesses, Gross					38,479
Business Combination, Consideration Transferred					$ 74,451
Business Acquisition, Effective Date of Acquisition					Jul. 31, 2014
Mountain West Bank | Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition Conversion Share Rate						0.2552
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	1,378,230				1,378,230
Business Acquisition, Share Price					$ 26.10