Loans and Allowance for Credit Losses - Outstanding Balances of Loan (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	$ 8,103	$ 16,136	$ 11,749	$ 26,612
Loans and Leases Receivable, Gross	4,334,214		4,334,214		4,283,833
Commercial, financial, agricultural and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	6,258	13,683	7,859	14,221
Loans and Leases Receivable, Gross	1,062,001		1,062,001		1,021,056
Real estate construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	296	671	296	755
Loans and Leases Receivable, Gross	100,709		100,709		93,289
Residential real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	640	321	1,735	643
Loans and Leases Receivable, Gross	1,238,791		1,238,791		1,262,718
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	157	694	297	9,238
Loans and Leases Receivable, Gross	1,306,752		1,306,752		1,296,472
Loans to individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	752	767	1,562	1,755
Loans and Leases Receivable, Gross	$ 625,961		$ 625,961		$ 610,298