Loans - Summary of Troubled Debt Restructuring by Loan Class, Defaulted under Restructured Terms (Detail)	Jun. 30, 2015 USD ($) Contract	Dec. 31, 2014 USD ($)	Jun. 30, 2014 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 14,000,000	$ 15,300,000	$ 21,100,000
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 12,467,000	12,759,000	$ 17,337,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	23		4
Troubled debt restructuring loans	$ 2,225,000		$ 130,000
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] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1
Troubled debt restructuring loans	$ 65,000
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 19,600,000	$ 24,600,000	$ 23,700,000
Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	6		14
Troubled debt restructuring loans	$ 297,000		$ 1,081,000
Commercial, Financial & Agricultural [Member] | Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	2
Troubled debt restructuring loans	$ 35,000
Real Estate - Construction & Development [Member] | Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract			1
Troubled debt restructuring loans			$ 35,000
Real Estate - Commercial & Farmland [Member] | Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	5
Troubled debt restructuring loans	$ 1,274,000
Real Estate - Commercial & Farmland [Member] | Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1		1
Troubled debt restructuring loans	$ 21,000		$ 71,000
Real Estate - Residential [Member] | Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	10		2
Troubled debt restructuring loans	$ 884,000		$ 72,000
Real Estate - Residential [Member] | Purchased Non-Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	1
Troubled debt restructuring loans	$ 65,000
Real Estate - Residential [Member] | Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	5		13
Troubled debt restructuring loans	$ 276,000		$ 1,010,000
Consumer Installment Loans [Member] | Excluding Purchased Non-Covered and Covered Loans [Member] | Financing Receivables, 1 to 29 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts | Contract	6		1
Troubled debt restructuring loans	$ 32,000		$ 23,000