Loans and Allowance for Loan Losses - Analysis of Information Pertaining to Impaired Loans, Excluding Purchased Non-Covered and Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 2,835,399	$ 2,457,444	$ 1,958,347
Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	319,654	244,373	174,217
Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	161,507	146,371	114,199
Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	907,524	808,323	732,322
Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	456,106	366,882	346,480
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	45,415	61,024
Recorded Investment With No Allowance	8,935	0
Recorded Investment With Allowance	25,552	46,417
Total impaired loans	34,487	46,417	57,629
Related Allowance	4,008	3,871
Average Recorded Investment	41,197	51,721
Excluding Purchased Non-Covered and Covered Loans [Member] \| Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	3,387	6,240
Recorded Investment With No Allowance	6	0
Recorded Investment With Allowance	1,956	4,618
Total impaired loans	1,962	4,618
Related Allowance	395	435
Average Recorded Investment	3,021	4,844
Excluding Purchased Non-Covered and Covered Loans [Member] \| Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	8,325	11,363
Recorded Investment With No Allowance	448	0
Recorded Investment With Allowance	4,005	5,867
Total impaired loans	4,453	5,867
Related Allowance	771	512
Average Recorded Investment	5,368	8,341
Excluding Purchased Non-Covered and Covered Loans [Member] \| Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	17,514	18,456
Recorded Investment With No Allowance	4,967	0
Recorded Investment With Allowance	9,651	15,479
Total impaired loans	14,618	15,479
Related Allowance	1,859	1,443
Average Recorded Investment	15,972	17,559
Excluding Purchased Non-Covered and Covered Loans [Member] \| Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	15,571	24,342
Recorded Investment With No Allowance	3,514	0
Recorded Investment With Allowance	9,407	19,970
Total impaired loans	12,921	19,970
Related Allowance	974	1,472
Average Recorded Investment	16,317	20,335
Excluding Purchased Non-Covered and Covered Loans [Member] \| Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	618	623
Recorded Investment With No Allowance		0
Recorded Investment With Allowance	533	483
Total impaired loans	533	483
Related Allowance	9	9
Average Recorded Investment	$ 519	$ 642

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5258-111524

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524

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