Loans - Summary of Trouble Debt Restructuring by Loan Class of Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015 Contract	Dec. 31, 2014	Mar. 31, 2014 Contract
Financing Receivable, Modifications [Line Items]
Number of contracts	14		10
Troubled debt restructuring loans	$ 1,519	$ 1,212	$ 2,241
Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	5
Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			2
Troubled debt restructuring loans			40
Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3		4
Troubled debt restructuring loans	746		1,897
Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6		3
Troubled debt restructuring loans	748		280
Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4		1
Troubled debt restructuring loans	20		24
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	23,300	24,600	27,800
Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	115	117	103
Troubled debt restructuring loans	20,721	22,619	22,775
Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	1
Troubled debt restructuring loans	3	40	14
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	4	3
Troubled debt restructuring loans	2,819	3,037	3,254
Covered Loans [Member] | Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	13	14	14
Troubled debt restructuring loans	6,461	8,079	7,461
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	97	96	85
Troubled debt restructuring loans	11,436	11,460	12,046
Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	2	3
Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	15	17	27
Troubled debt restructuring loans	2,570	1,942	5,025
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	2	5
Troubled debt restructuring loans			68
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	5
Troubled debt restructuring loans	13	29	49
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	5	7
Troubled debt restructuring loans	1,736	1,082	3,872
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10	8	9
Troubled debt restructuring loans	821	831	1,031
Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			1
Troubled debt restructuring loans			$ 5