Loans and Allowance for Loan Losses (Granite Purchased Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015		Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable [Line Items]
Total Loans	$ 1,525,070		$ 1,543,795	[1]
Granite Corp [Member]
Financing Receivable [Line Items]
Purchased Impaired	72,598	$ 84,627	87,564		$ 102,115	$ 109,262	$ 122,842
Purchased Contractual	16,869		18,153
Total Loans	89,467		105,717
Unpaid Principal Balance	88,869		106,466
Granite Corp [Member] | Commercial and Agricultural [Member]
Financing Receivable [Line Items]
Purchased Impaired	4,607		4,995
Purchased Contractual	114		238
Total Loans	4,721		5,233
Unpaid Principal Balance	3,589		4,149
Granite Corp [Member] | Real estate - construction [Member]
Financing Receivable [Line Items]
Purchased Impaired	7,035		7,744
Purchased Contractual	0		0
Total Loans	7,035		7,744
Unpaid Principal Balance	7,763		8,579
Granite Corp [Member] | Real estate - mortgage, 1-4 family residential [Member]
Financing Receivable [Line Items]
Purchased Impaired	12,405		13,917
Purchased Contractual	16,755		17,915
Total Loans	29,160		31,832
Unpaid Principal Balance	29,609		32,558
Granite Corp [Member] | Real estate - mortgage, commercial [Member]
Financing Receivable [Line Items]
Purchased Impaired	47,728		59,989
Purchased Contractual	0		0
Total Loans	47,728		59,989
Unpaid Principal Balance	47,383		60,582
Granite Corp [Member] | Consumer [Member]
Financing Receivable [Line Items]
Purchased Impaired	823		919
Purchased Contractual	0		0
Total Loans	823		919
Unpaid Principal Balance	$ 525		$ 598

[1] Derived from audited consolidated financial statements