Loans - Summary of Credit Quality Indicate Financial Receivable (Covered Loan Portfolio) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	$ 1,999,420	$ 1,889,881	$ 1,695,382
Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	334,917	319,654	270,571
Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	178,568	161,507	149,543
Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	947,274	907,524	836,230
Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	496,043	456,106	393,001
Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	29,113	30,782	32,345
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	245,745	271,279	372,694
Covered Loans [Member] | 15 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	3,770	1,287	1,684
Covered Loans [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	34,947	41,434	64,918
Covered Loans [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	25,560	18,747	23,454
Covered Loans [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	113,771	128,082	156,233
Covered Loans [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	26,596	20,913	30,944
Covered Loans [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	41,101	60,816	95,461
Covered Loans [Member] | Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	20,905	21,467	24,813
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 15 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	667
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	75	917	1,769
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	4,481	164	139
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	5,094	5,181	6,921
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	10,588	4,808	5,106
Covered Loans [Member] | Commercial, Financial & Agricultural [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade		10,397	10,878
Covered Loans [Member] | Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	19,519	23,447	41,434
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 15 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	1,847	1	10
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	458	3,184	7,760
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	8,567	537	978
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	2,594	9,406	9,182
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	6,053	2,753	1,185
Covered Loans [Member] | Real Estate - Construction & Development [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade		7,566	22,319
Covered Loans [Member] | Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	130,290	147,627	214,649
Covered Loans [Member] | Commercial And Farmland [Member] | 15 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	734	761	1,024
Covered Loans [Member] | Commercial And Farmland [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	21,010	23,167	35,625
Covered Loans [Member] | Commercial And Farmland [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	6,382	11,404	17,416
Covered Loans [Member] | Commercial And Farmland [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	69,536	80,334	101,948
Covered Loans [Member] | Commercial And Farmland [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	4,053	5,302	17,625
Covered Loans [Member] | Commercial And Farmland [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	28,575	26,659	41,011
Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	74,847	78,520	91,372
Covered Loans [Member] | Real Estate - Residential [Member] | 15 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	522	525	650
Covered Loans [Member] | Real Estate - Residential [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	13,353	14,089	19,613
Covered Loans [Member] | Real Estate - Residential [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	6,130	6,642	4,870
Covered Loans [Member] | Real Estate - Residential [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	36,510	33,124	38,140
Covered Loans [Member] | Real Estate - Residential [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	5,893	8,050	7,025
Covered Loans [Member] | Real Estate - Residential [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	12,439	16,090	21,074
Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	184	218	426
Covered Loans [Member] | Consumer Installment Loans [Member] | 20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	51	77	151
Covered Loans [Member] | Consumer Installment Loans [Member] | 23 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade			51
Covered Loans [Member] | Consumer Installment Loans [Member] | 25 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	37	37	42
Covered Loans [Member] | Consumer Installment Loans [Member] | 30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	9		3
Covered Loans [Member] | Consumer Installment Loans [Member] | 40 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans portfolio by risk grade	$ 87	$ 104	$ 179