Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 21,157	$ 22,377	$ 22,377
Provision for loan losses	1,069us-gaap_ProvisionForLoanAndLeaseLosses	1,726us-gaap_ProvisionForLoanAndLeaseLosses	5,648us-gaap_ProvisionForLoanAndLeaseLosses
Loans charged off	(1,648)	(2,104)	(9,560)
Recoveries of loans previously charged off	1,274	745	2,692
Ending balance	21,852	22,744	21,157
Loans individually evaluated for impairment	4,817	4,076	3,890
Loans collectively evaluated for impairment	17,035	18,668	17,267
Individually evaluated for impairment	28,987	38,088	27,649
Collectively evaluated for impairment	2,631,383	2,208,496	2,563,652
Acquired with deteriorated credit quality	227,887	258,761	244,098
Ending balance	2,888,257	2,505,345	2,835,399
Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	(432)		84
Loans charged off	(230)		(84)
Recoveries of loans previously charged off	662
Collectively evaluated for impairment	552,837	383,709	579,172
Acquired with deteriorated credit quality	90,255	53,560	95,067
Ending balance	29,616	35,136	33,989
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses	401	225	843
Loans charged off	(563)	(498)	(1,851)
Recoveries of loans previously charged off	162	273	1,008
Collectively evaluated for impairment	108,113	167,493	122,248
Acquired with deteriorated credit quality	137,632	205,201	149,031
Ending balance	97,212	164,467	95,967
Commercial, Financial & Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,004	1,823	1,823
Provision for loan losses	(498)	1,090	1,427
Loans charged off	(392)	(743)	(1,567)
Recoveries of loans previously charged off	285	49	321
Ending balance	1,399	2,219	2,004
Loans individually evaluated for impairment	230	318	375
Loans collectively evaluated for impairment	1,169	1,901	1,629
Individually evaluated for impairment	324	2,837	490
Collectively evaluated for impairment	334,593	267,734	319,164
Ending balance	334,917	270,571	319,654
Commercial, Financial & Agricultural [Member] \| Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	1,331	233	1,366
Commercial, Financial & Agricultural [Member] \| Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	13,512	16,020	14,385
Real Estate - Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,030	5,538	5,538
Provision for loan losses	347	337	(265)
Loans charged off	(97)	(65)	(592)
Recoveries of loans previously charged off	31	108	349
Ending balance	5,311	5,918	5,030
Loans individually evaluated for impairment	627	631	743
Loans collectively evaluated for impairment	4,684	5,287	4,287
Individually evaluated for impairment	2,982	3,817	3,709
Collectively evaluated for impairment	175,586	145,726	157,798
Ending balance	178,568	149,543	161,507
Real Estate - Construction & Development [Member] \| Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	2,153	6,173	5,161
Real Estate - Construction & Development [Member] \| Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	24,503	50,876	27,289
Commercial And Farmland [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,823	8,393	8,393
Provision for loan losses	(56)	622	3,444
Loans charged off	(12)	(533)	(3,288)
Recoveries of loans previously charged off	15	143	274
Ending balance	8,770	8,625	8,823
Loans individually evaluated for impairment	2,123	1,994	1,861
Loans collectively evaluated for impairment	6,647	6,631	6,962
Individually evaluated for impairment	14,557	16,832	14,546
Collectively evaluated for impairment	932,717	819,398	892,978
Ending balance	947,274	836,230	907,524
Commercial And Farmland [Member] \| Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	13,911	12,966	15,007
Commercial And Farmland [Member] \| Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	35,493	66,557	31,309
Real Estate - Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	4,129	6,034	6,034
Provision for loan losses	1,090	(656)	(452)
Loans charged off	(268)	(181)	(1,707)
Recoveries of loans previously charged off	57	83	254
Ending balance	5,008	5,280	4,129
Loans individually evaluated for impairment	1,837	1,133	911
Loans collectively evaluated for impairment	3,171	4,147	3,218
Individually evaluated for impairment	11,124	14,602	8,904
Collectively evaluated for impairment	484,919	378,399	447,202
Ending balance	496,043	393,001	456,106
Real Estate - Residential [Member] \| Purchased Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	12,183	15,524	12,283
Real Estate - Residential [Member] \| Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending balance	23,585	30,824	22,860
Consumer Installment Loans and Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,171	589	589
Provision for loan losses	217	108	567
Loans charged off	(86)	(84)	(471)
Recoveries of loans previously charged off	62	89	486
Ending balance	1,364	702	1,171
Loans collectively evaluated for impairment	1,364	702	1,171
Collectively evaluated for impairment	42,618	46,037	45,090
Ending balance	$ 42,618	$ 46,037	$ 45,090

The balance of financing receivables that were acquired with deteriorated credit quality.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

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-Publisher FASB

-Name Accounting Standards Codification

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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-Publisher FASB

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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-Publisher FASB

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Amount of direct write-downs of financing receivables charged against the allowance.

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The balance of financing receivables that were collectively evaluated for impairment.

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

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-Number 210

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