Acquisitions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands					6 Months Ended	12 Months Ended
	May. 28, 2015	May. 14, 2015	Apr. 15, 2015	Jan. 16, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Business Acquisition [Line Items]
Assets					$ 6,717,007	$ 6,051,812	$ 5,913,918
Loans outstanding					4,404,209	3,836,554
Deposits					5,317,269	4,768,022
Nonaccrual loans					25,894	24,205
Premier Valley Bank
Business Acquisition [Line Items]
Purchase price in cash	$ 95,000
Purchase price (in usd per share)	$ 7.73
Payment in common stock, percentage	70.00%
Payment in cash, percentage	30.00%
Assets					655,000
Loans outstanding					413,000
Deposits					573,000
First Scottsdale Bank, N.A.
Business Acquisition [Line Items]
Purchase price in cash		$ 17,700
Assets					96,000
Loans outstanding					63,000
Deposits					79,000
Community Bancorporation of New Mexico, Inc.
Business Acquisition [Line Items]
Purchase price in cash			$ 11,100
Assets					175,000
Loans outstanding					109,000
Deposits					146,000
Community Banc-Corp of Sheboygan, Inc.
Business Acquisition [Line Items]
Purchase price in cash				$ 6
Assets				506,800
Loans outstanding				395,000
Deposits				$ 433,900
Purchase price, percentage of adjusted tangible book value				155.00%
Total purchase price				$ 53,058
Purchase price paid by delivery of shares of common stock				1,970,720
Pre-tax merger related expenses					$ 1,700	$ 1,700
Nonaccrual loans				$ 5,800