Acquisitions (Narrative) (Details) - USD ($) $ in Thousands						9 Months Ended
	Feb. 05, 2016	Nov. 30, 2015	Sep. 11, 2015	Aug. 21, 2015	Jan. 16, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Business Acquisition [Line Items]
Assets						$ 8,202,215	$ 7,694,754	$ 6,805,884
Deposits						6,912,693	6,405,823
Goodwill						127,699	97,852
Nonaccrual loans						57,344	37,874
Premises, furniture and equipment held for sale						3,634	$ 3,889
CIC Bancshares, Inc.
Business Acquisition [Line Items]
Total purchase price	$ 76,882
Purchase price paid by delivery of shares of common stock (shares)	2,003,235
Purchase price in cash	$ 15,672
Other borrowings	7,924
Assets	772,600
Loans	581,500
Deposits	648,100
Goodwill	29,848
Pre-tax merger related expenses						$ 551
Nonaccrual loans	1,600
Loans held to maturity	581,477
CIC Bancshares, Inc. | Preferred Stock
Business Acquisition [Line Items]
Convertible preferred stock issue, fair value	$ 3,800
Premier Valley Bank
Business Acquisition [Line Items]
Total purchase price		$ 95,500
Purchase price paid by delivery of shares of common stock (shares)		1,758,543
Purchase price in cash		$ 28,500
Assets		692,700
Loans		389,800
Deposits		622,700
Goodwill		41,000
Loans held to maturity		$ 389,800
First Scottsdale Bank, N.A.
Business Acquisition [Line Items]
Purchase price in cash			$ 17,700
Assets			81,200
Deposits			65,900
Goodwill			2,500
Loans held to maturity			$ 54,700
Community Bancorporation of New Mexico, Inc.
Business Acquisition [Line Items]
Purchase price in cash				$ 11,100
Assets				166,300
Deposits				147,400
Goodwill				213
Loans held to maturity				99,500
Premises, furniture and equipment held for sale				$ 3,400
Community Banc-Corp of Sheboygan, Inc.
Business Acquisition [Line Items]
Total purchase price					$ 53,100
Purchase price paid by delivery of shares of common stock (shares)					1,970,720
Assets					$ 506,800
Deposits					433,900
Goodwill					18,600
Loans held to maturity					$ 395,000
Purchase price, percentage of adjusted tangible book value					155.00%