Loans and Allowance for Loan Losses - Summary of Trouble Debt Restructuring by Loan Class of Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014 Contract	Dec. 31, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of contracts	14	10
Troubled debt restructuring loans	$ 1,214	$ 3,390
Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	3
Troubled debt restructuring loans	236	525
Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	33	29
Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	3
Troubled debt restructuring loans	570	2,197
Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	3
Troubled debt restructuring loans	314	639
Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Troubled debt restructuring loans	61
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	24,600	27,300
Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	117	100
Troubled debt restructuring loans	22,619	22,243
Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	1
Troubled debt restructuring loans	40	13
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	3
Troubled debt restructuring loans	3,037	3,256
Covered Loans [Member] | Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	14	13
Troubled debt restructuring loans	8,079	7,255
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	96	83
Troubled debt restructuring loans	11,460	11,719
Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	3
Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	17	24
Troubled debt restructuring loans	1,942	5,021
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	5
Troubled debt restructuring loans		71
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	4
Troubled debt restructuring loans	29	52
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	5
Troubled debt restructuring loans	1,082	3,946
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8	8
Troubled debt restructuring loans	831	942
Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		2
Troubled debt restructuring loans		$ 10