Loans - Summary of Troubled Debt Restructurings by Loan Class, Excluding Purchased Non-Covered and 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
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	12,935	12,759	18,848
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	86	92	80
Troubled debt restructuring loans	12,935	12,759	18,848
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	6	4
Troubled debt restructuring loans	277	290	711
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	9	11
Troubled debt restructuring loans	789	679	1,953
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	20	19	19
Troubled debt restructuring loans	7,309	6,477	8,733
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	42	47	35
Troubled debt restructuring loans	4,513	5,258	7,364
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10	11	11
Troubled debt restructuring loans	47	55	87
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	34	32	18
Troubled debt restructuring loans	997	2,523	2,365
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	2	2
Troubled debt restructuring loans	17	13	40
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	5	1
Troubled debt restructuring loans	90	228	29
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	3	5
Troubled debt restructuring loans	64	724	1,316
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	11	8
Troubled debt restructuring loans	736	1,485	961
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	15	11	2
Troubled debt restructuring loans	$ 90	$ 73	$ 19