Loans and Allowance for Loan Losses - Summary of Carrying Value of Purchased Non-Covered Loans According to Loan Type (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	$ 21,157	$ 22,377
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	674,239	448,753
Purchased Non-Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	38,041	32,141
Purchased Non-Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	58,362	31,176
Purchased Non-Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	306,706	179,898
Purchased Non-Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	266,342	200,851
Purchased Non-Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	$ 4,788	$ 4,687