Loans and Allowance for Loan Losses - Summary of Financial Receivable Nonaccrual Basis (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 21,728,000	$ 29,203,000	$ 38,885,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	1,672,000	4,103,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	3,774,000	3,971,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	8,141,000	8,566,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	7,663,000	12,152,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	478,000	411,000
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	18,249,000	6,659,000
Purchased Non-Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	175,000	11,000
Purchased Non-Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	1,119,000	325,000
Purchased Non-Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	10,242,000	1,653,000
Purchased Non-Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	6,644,000	4,658,000
Purchased Non-Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	69,000	12,000
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	35,412,000	69,152,000
Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	8,541,000	7,257,000
Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	7,601,000	14,781,000
Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	12,584,000	33,495,000
Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	6,595,000	13,278,000
Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 91,000	$ 341,000