Loans - Summary of Financial Receivable Nonaccrual Basis (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 20,841,000	$ 21,728,000	$ 26,729,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	1,015,000	1,672,000	3,008,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	3,286,000	3,774,000	4,080,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	7,893,000	8,141,000	8,550,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	8,246,000	7,663,000	10,631,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	401,000	478,000	460,000
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	17,308,000	18,249,000	15,318,000
Purchased Non-Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	198,000	175,000	117,000
Purchased Non-Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	785,000	1,119,000	1,131,000
Purchased Non-Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	9,096,000	10,242,000	6,829,000
Purchased Non-Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	7,202,000	6,644,000	7,208,000
Purchased Non-Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	27,000	69,000	33,000
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	38,359,000	35,412,000	59,781,000
Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	8,404,000	8,541,000	10,025,000
Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	6,262,000	7,601,000	14,780,000
Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	17,000,000	12,584,000	24,285,000
Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	6,606,000	6,595,000	10,558,000
Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 87,000	$ 91,000	$ 133,000