Loans and Allowance for Loan Losses (Granite Purchased Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015		Mar. 31, 2015	Dec. 31, 2014
Financing Receivable [Line Items]
Total Loans	$ 1,524,406	$ 1,543,795	[1]
Granite Corp [Member]
Financing Receivable [Line Items]
Purchased Impaired	84,627	87,564		$ 109,262	$ 122,842
Purchased Contractual	17,626	18,153
Total Loans	102,253	105,717
Unpaid Principal Balance	101,798	106,466
Granite Corp [Member] | Commercial and Agricultural [Member]
Financing Receivable [Line Items]
Purchased Impaired	4,751	4,995
Purchased Contractual	156	238
Total Loans	4,907	5,233
Unpaid Principal Balance	3,848	4,149
Granite Corp [Member] | Real estate - construction [Member]
Financing Receivable [Line Items]
Purchased Impaired	7,274	7,744
Purchased Contractual	0	0
Total Loans	7,274	7,744
Unpaid Principal Balance	8,070	8,579
Granite Corp [Member] | Real estate - mortgage, 1-4 family residential [Member]
Financing Receivable [Line Items]
Purchased Impaired	13,420	13,917
Purchased Contractual	17,470	17,915
Total Loans	30,890	31,832
Unpaid Principal Balance	31,442	32,558
Granite Corp [Member] | Real estate - mortgage, commercial [Member]
Financing Receivable [Line Items]
Purchased Impaired	58,321	59,989
Purchased Contractual	0	0
Total Loans	58,321	59,989
Unpaid Principal Balance	57,885	60,582
Granite Corp [Member] | Consumer [Member]
Financing Receivable [Line Items]
Purchased Impaired	861	919
Purchased Contractual	0	0
Total Loans	861	919
Unpaid Principal Balance	$ 553	$ 598

[1] Derived from audited consolidated financial statements