Loans - Summary of Troubled Debt Restructurings by Loan Class of Purchased Non-covered Loans (Detail)	Jun. 30, 2015 USD ($) Contract	Dec. 31, 2014 USD ($) Contract	Jun. 30, 2014 USD ($)
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 14,000,000	$ 15,300,000	$ 21,100,000
Purchased Non-Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 6,792,000	$ 1,212,000	$ 0
Purchased Non-Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	24	9
Troubled debt restructuring loans	$ 6,792,000	$ 1,212,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	3	1
Troubled debt restructuring loans	$ 374,000	$ 317,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	7	1
Troubled debt restructuring loans	$ 4,058,000	$ 346,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	12	6
Troubled debt restructuring loans	$ 2,354,000	$ 547,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	2	1
Troubled debt restructuring loans	$ 6,000	$ 2,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	6	1
Troubled debt restructuring loans	$ 166,000	$ 25,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1
Troubled debt restructuring loans	$ 1,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial & Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1
Troubled debt restructuring loans	$ 69,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	2	1
Troubled debt restructuring loans	$ 91,000	$ 25,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	2
Troubled debt restructuring loans	$ 5,000