Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 21,852	$ 22,212	$ 22,744	$ 21,157	$ 22,377	$ 22,377
Provision for loan losses	2,656	888	1,365	3,725	3,091	5,648
Loans charged off	(3,542)	(2,488)	(2,614)	(5,190)	(4,718)	(9,560)
Recoveries of loans previously charged off	692	545	759	1,966	1,504	2,692
Ending balance	21,658	21,157	22,254	21,658	22,254	21,157
Loans individually evaluated for impairment	3,892	3,890	3,445	3,892	3,445	3,890
Loans collectively evaluated for impairment	17,766	17,267	18,809	17,766	18,809	17,267
Individually evaluated for impairment	27,885	27,649	32,522	27,885	32,522	27,649
Collectively evaluated for impairment	2,932,971	2,563,652	2,499,031	2,932,971	2,499,031	2,563,652
Loan pools collectively evaluated for impairment	268,984			268,984
Ending balance	3,458,495	2,835,399	2,803,440	3,458,495	2,803,440	2,835,399
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Acquired with deteriorated credit quality	228,655	244,098	271,887	228,655	271,887	244,098
Purchased Non Covered Loans Including Pools [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	121	80		(311)		84
Loans charged off	(240)	(80)		(470)		(84)
Recoveries of loans previously charged off	119			781
Collectively evaluated for impairment	698,068	579,172	608,874	698,068	608,874	579,172
Loan pools collectively evaluated for impairment	268,984			268,984
Ending balance	1,077,297	674,239	702,131	1,077,297	702,131	674,239
Purchased Non Covered Loans Including Pools [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Acquired with deteriorated credit quality	110,245	95,067	93,257	110,245	93,257	95,067
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	735	158	368	1,136	593	843
Loans charged off	(850)	(337)	(641)	(1,413)	(1,139)	(1,851)
Recoveries of loans previously charged off	115	179	273	277	546	1,008
Collectively evaluated for impairment	91,188	122,248	152,620	91,188	152,620	122,248
Ending balance	99,932	95,967	77,392	99,932	77,392	95,967
Covered Loans [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Acquired with deteriorated credit quality	118,410	149,031	178,630	118,410	178,630	149,031
Commercial, Financial & Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,399	2,581	2,219	2,004	1,823	1,823
Provision for loan losses	322	(200)	(3)	(176)	1,087	1,427
Loans charged off	(410)	(468)	(165)	(802)	(908)	(1,567)
Recoveries of loans previously charged off	115	91	134	400	183	321
Ending balance	1,426	2,004	2,185	1,426	2,185	2,004
Loans individually evaluated for impairment	450	375	282	450	282	375
Loans collectively evaluated for impairment	976	1,629	1,903	976	1,903	1,629
Individually evaluated for impairment	3,351	490	855	3,351	855	490
Collectively evaluated for impairment	369,851	319,164	303,733	369,851	303,733	319,164
Ending balance	373,202	319,654	304,588	373,202	304,588	319,654
Commercial, Financial & Agricultural [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	14,260	14,385	14,694	14,260	14,694	14,385
Real Estate - Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,311	5,294	5,918	5,030	5,538	5,538
Provision for loan losses	40	(239)	(426)	387	(89)	(265)
Loans charged off	(263)	(74)	(157)	(360)	(222)	(592)
Recoveries of loans previously charged off	277	49	96	308	204	349
Ending balance	5,365	5,030	5,431	5,365	5,431	5,030
Loans individually evaluated for impairment	414	743	710	414	710	743
Loans collectively evaluated for impairment	4,951	4,287	4,721	4,951	4,721	4,287
Individually evaluated for impairment	1,437	3,709	3,264	1,437	3,264	3,709
Collectively evaluated for impairment	203,582	157,798	146,082	203,582	146,082	157,798
Ending balance	205,019	161,507	149,346	205,019	149,346	161,507
Real Estate - Construction & Development [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	29,895	27,289	12,921	29,895	12,921	27,289
Real Estate - Commercial & Farmland [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,770	8,632	8,625	8,823	8,393	8,393
Provision for loan losses	756	1,133	452	700	1,074	3,444
Loans charged off	(1,162)	(1,033)	(769)	(1,174)	(1,302)	(3,288)
Recoveries of loans previously charged off	17	91	9	32	152	274
Ending balance	8,381	8,823	8,317	8,381	8,317	8,823
Loans individually evaluated for impairment	1,242	1,861	1,652	1,242	1,652	1,861
Loans collectively evaluated for impairment	7,139	6,962	6,665	7,139	6,665	6,962
Individually evaluated for impairment	15,028	14,546	16,865	15,028	16,865	14,546
Collectively evaluated for impairment	995,167	892,978	833,135	995,167	833,135	892,978
Ending balance	1,010,195	907,524	850,000	1,010,195	850,000	907,524
Real Estate - Commercial & Farmland [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	37,426	31,309	27,742	37,426	27,742	31,309
Real Estate - Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,008	5,407	5,280	4,129	6,034	6,034
Provision for loan losses	234	(981)	590	1,324	(66)	(452)
Loans charged off	(464)	(368)	(752)	(732)	(933)	(1,707)
Recoveries of loans previously charged off	27	71	48	84	131	254
Ending balance	4,805	4,129	5,166	4,805	5,166	4,129
Loans individually evaluated for impairment	1,786	911	801	1,786	801	911
Loans collectively evaluated for impairment	3,019	3,218	4,365	3,019	4,365	3,218
Individually evaluated for impairment	8,069	8,904	11,538	8,069	11,538	8,904
Collectively evaluated for impairment	529,132	447,202	411,193	529,132	411,193	447,202
Ending balance	537,201	456,106	422,731	537,201	422,731	456,106
Real Estate - Residential [Member] | Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	18,226	22,860	21,874	18,226	21,874	22,860
Consumer Installment Loans and Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,364	298	702	1,171	589	589
Provision for loan losses	448	937	384	665	492	567
Loans charged off	(153)	(128)	(130)	(239)	(214)	(471)
Recoveries of loans previously charged off	22	64	199	84	288	486
Ending balance	1,681	1,171	1,155	1,681	1,155	1,171
Loans collectively evaluated for impairment	1,681	1,171	1,155	1,681	1,155	1,171
Collectively evaluated for impairment	45,983	45,090	43,394	45,983	43,394	45,090
Ending balance	$ 45,983	$ 45,090	$ 43,394	$ 45,983	$ 43,394	$ 45,090