Loans - Summary of Purchased Non-Covered Loans According to Major Loan Type (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	$ 21,852	$ 21,157	$ 22,744
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	643,092	674,239	437,269
Purchased Non-Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	36,258	38,041	30,810
Purchased Non-Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	53,668	58,362	31,820
Purchased Non-Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	291,760	306,706	174,281
Purchased Non-Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	257,216	266,342	196,078
Purchased Non-Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total non-covered loans	$ 4,190	$ 4,788	$ 4,280