Loans - Summary of Troubled Debt Restructurings by Loan Class (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
Purchased Non-Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	1,526	1,212	5,191
Purchased Non-Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10	9	22
Troubled debt restructuring loans	1,526	1,212	5,191
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	7
Troubled debt restructuring loans	328	317	2,443
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	1	2
Troubled debt restructuring loans	720	346	961
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	6	12
Troubled debt restructuring loans	477	547	1,779
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	1
Troubled debt restructuring loans	1	2	8
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	1	11
Troubled debt restructuring loans	167	25	1,268
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		1
Troubled debt restructuring loans	1		6
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			2
Troubled debt restructuring loans			264
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		2
Troubled debt restructuring loans	69		726
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	1	4
Troubled debt restructuring loans	93	25	255
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		2
Troubled debt restructuring loans	$ 4		$ 17