Loans - Summary of Troubled Debt Restructurings by Loan Class, Excluding Purchased Non-Covered and 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
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 12,467	$ 12,759	$ 17,337
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	94	92	86
Troubled debt restructuring loans	$ 12,467	$ 12,759	$ 17,337
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	6	6	3
Troubled debt restructuring loans	$ 278	$ 290	$ 257
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	11	9	12
Troubled debt restructuring loans	$ 821	$ 679	$ 2,080
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	17	19	19
Troubled debt restructuring loans	$ 6,617	$ 6,477	$ 7,590
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	49	47	38
Troubled debt restructuring loans	$ 4,702	$ 5,258	$ 7,335
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	11	11	14
Troubled debt restructuring loans	$ 49	$ 55	$ 75
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	43	32	22
Troubled debt restructuring loans	$ 1,549	$ 2,523	$ 3,743
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	5	2	3
Troubled debt restructuring loans	$ 29	$ 13	$ 465
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 | Contract	3	5	2
Troubled debt restructuring loans	$ 57	$ 228	$ 32
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	3	3	4
Troubled debt restructuring loans	$ 598	$ 724	$ 2,151
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	15	11	8
Troubled debt restructuring loans	$ 783	$ 1,485	$ 1,044
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	17	11	5
Troubled debt restructuring loans	$ 82	$ 73	$ 51