Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 22,254	$ 24,217	$ 22,377	$ 23,593	$ 23,593
Provision for loan losses	1,669	2,920	4,760	10,008	11,486
Loans charged off	(2,355)	(3,928)	(7,072)	(10,954)	(14,823)
Recoveries of loans previously charged off	644	645	2,147	1,207	2,121
Ending balance	22,212	23,854	22,212	23,854	22,377
Loans individually evaluated for impairment	4,105	4,849	4,105	4,849	3,585
Loans collectively evaluated for impairment	18,107	19,005	18,107	19,005	18,792
Individually evaluated for impairment	33,616	38,705	33,616	38,705	39,203
Collectively evaluated for impairment	2,538,994	1,736,622	2,538,994	1,736,622	2,134,029
Acquired with deteriorated credit quality	263,462	231,589	263,462	231,589	284,212
Ending balance	2,836,072	2,006,916	2,836,072	2,006,916	2,457,444
Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	4		4
Loans charged off	(4)		(4)
Collectively evaluated for impairment	581,723		581,723		381,588
Acquired with deteriorated credit quality	92,001		92,001		67,165
Ending balance	26,380		26,380		10,996
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	92	471	685	1,261	1,539
Loans charged off	(376)	(471)	(1,514)	(1,261)	(1,539)
Recoveries of loans previously charged off	284		829
Collectively evaluated for impairment	142,128	186,060	142,128	186,060	173,190
Acquired with deteriorated credit quality	171,461	231,589	171,461	231,589	217,047
Ending balance	71,713	115,633	71,713	115,633	106,690
Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,185	2,951	1,823	2,439	2,439
Provision for loan losses	540	(107)	1,627	1,011	711
Loans charged off	(191)	(482)	(1,099)	(1,216)	(1,759)
Recoveries of loans previously charged off	47	212	230	340	432
Ending balance	2,581	2,574	2,581	2,574	1,823
Loans individually evaluated for impairment	611	741	611	741	356
Loans collectively evaluated for impairment	1,970	1,833	1,970	1,833	1,467
Individually evaluated for impairment	1,549	3,657	1,549	3,657	3,457
Collectively evaluated for impairment	333,234	241,334	333,234	241,334	240,916
Ending balance	334,783	244,991	334,783	244,991	244,373
Commercial, Financial and Agricultural [Member] | Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	438		438		19
Commercial, Financial and Agricultural [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	11,356	10,645	11,356	10,645	9,680
Real Estate - Construction and Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,431	5,642	5,538	5,343	5,343
Provision for loan losses	63	601	(26)	2,127	1,742
Loans charged off	(296)	(367)	(518)	(1,598)	(2,020)
Recoveries of loans previously charged off	96	84	300	88	473
Ending balance	5,294	5,960	5,294	5,960	5,538
Loans individually evaluated for impairment	540	682	540	682	407
Loans collectively evaluated for impairment	4,754	5,278	4,754	5,278	5,131
Individually evaluated for impairment	3,078	3,524	3,078	3,524	3,581
Collectively evaluated for impairment	151,237	128,753	151,237	128,753	142,790
Ending balance	154,315	132,277	154,315	132,277	146,371
Real Estate - Construction and Development [Member] | Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	3,794		3,794		542
Real Estate - Construction and Development [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	13,268	25,401	13,268	25,401	20,915
Real Estate - Commercial and Farmland [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,317	8,797	8,393	9,157	9,157
Provision for loan losses	1,237	1,212	2,311	2,632	2,777
Loans charged off	(953)	(1,080)	(2,255)	(2,873)	(3,571)
Recoveries of loans previously charged off	31	5	183	18	30
Ending balance	8,632	8,934	8,632	8,934	8,393
Loans individually evaluated for impairment	1,682	1,997	1,682	1,997	1,427
Loans collectively evaluated for impairment	6,950	6,937	6,950	6,937	6,966
Individually evaluated for impairment	17,129	14,605	17,129	14,605	15,240
Collectively evaluated for impairment	865,031	784,544	865,031	784,544	793,083
Ending balance	882,160	799,149	882,160	799,149	808,323
Real Estate - Commercial and Farmland [Member] | Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	12,354		12,354		2,673
Real Estate - Commercial and Farmland [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	26,624	51,105	26,624	51,105	46,612
Real Estate - Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,166	6,360	6,034	5,898	5,898
Provision for loan losses	595	626	529	2,966	4,463
Loans charged off	(406)	(1,323)	(1,339)	(3,430)	(5,215)
Recoveries of loans previously charged off	52	291	183	520	888
Ending balance	5,407	5,954	5,407	5,954	6,034
Loans individually evaluated for impairment	1,272	1,429	1,272	1,429	1,395
Loans collectively evaluated for impairment	4,135	4,525	4,135	4,525	4,639
Individually evaluated for impairment	11,860	16,919	11,860	16,919	16,925
Collectively evaluated for impairment	424,655	339,001	424,655	339,001	349,957
Ending balance	436,515	355,920	436,515	355,920	366,882
Real Estate - Residential [Member] | Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	9,610		9,610		7,712
Real Estate - Residential [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	20,331	28,078	20,331	28,078	29,089
Consumer Installment Loans and Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,155	467	589	756	756
Provision for loan losses	(862)	117	(370)	11	254
Loans charged off	(129)	(205)	(343)	(576)	(719)
Recoveries of loans previously charged off	134	53	422	241	298
Ending balance	298	432	298	432	589
Loans collectively evaluated for impairment	298	432	298	432	589
Collectively evaluated for impairment	40,986	56,930	40,986	56,930	52,505
Ending balance	$ 40,986	$ 56,930	$ 40,986	$ 56,930	$ 52,505