Loans - Summary of Trouble Debt Restructuring by Loan Class of Covered Loans (Detail) $ in Thousands	Jun. 30, 2015 USD ($) Contract	Dec. 31, 2014 USD ($) Contract	Jun. 30, 2014 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 14,000	$ 15,300	$ 21,100
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 19,600	$ 24,600	$ 23,700
Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	111	117	110
Troubled debt restructuring loans	$ 17,500	$ 22,619	$ 21,102
Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1	2	1
Troubled debt restructuring loans	$ 3	$ 40	$ 12
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	3	4	4
Troubled debt restructuring loans	$ 2,832	$ 3,037	$ 3,020
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	11	14	13
Troubled debt restructuring loans	$ 3,973	$ 8,079	$ 6,979
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	95	96	92
Troubled debt restructuring loans	$ 10,690	$ 11,460	$ 11,091
Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1	1
Troubled debt restructuring loans	$ 2	$ 3
Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	20	17	33
Troubled debt restructuring loans	$ 2,059	$ 1,942	$ 2,563
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	2	2	4
Troubled debt restructuring loans	$ 0		$ 27
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1	2	5
Troubled debt restructuring loans	$ 13	$ 29	$ 74
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	3	5	7
Troubled debt restructuring loans	$ 1,105	$ 1,082	$ 1,388
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	14	8	16
Troubled debt restructuring loans	$ 941	$ 831	$ 1,070
Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract			1
Troubled debt restructuring loans			$ 4