Loans and Allowance for Loan Losses - Analysis of Information Pertaining to Purchased Non-Covered Impaired 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
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	26,885	19,970
Recorded Investment With No Allowance	19,461	12,597
Recorded Investment With Allowance	0	0
Total Recorded Investment	19,461	12,597
Related Allowance	0	0
Average Recorded Investment	16,444	242
Purchased Non-Covered Loans [Member] \| Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	499	19
Recorded Investment With No Allowance	175	11
Recorded Investment With Allowance	0	0
Total Recorded Investment	175	11
Related Allowance	0	0
Average Recorded Investment	165	0
Purchased Non-Covered Loans [Member] \| Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	2,210	5,719
Recorded Investment With No Allowance	1,436	3,690
Recorded Investment With Allowance	0	0
Total Recorded Investment	1,436	3,690
Related Allowance	0	0
Average Recorded Investment	1,643	71
Purchased Non-Covered Loans [Member] \| Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	13,520	4,563
Recorded Investment With No Allowance	10,588	2,881
Recorded Investment With Allowance	0	0
Total Recorded Investment	10,588	2,881
Related Allowance	0	0
Average Recorded Investment	7,484	55
Purchased Non-Covered Loans [Member] \| Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	10,487	9,612
Recorded Investment With No Allowance	7,191	5,978
Recorded Investment With Allowance	0	0
Total Recorded Investment	7,191	5,978
Related Allowance	0	0
Average Recorded Investment	7,084	115
Purchased Non-Covered Loans [Member] \| Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	169	57
Recorded Investment With No Allowance	71	37
Recorded Investment With Allowance	0	0
Total Recorded Investment	71	37
Related Allowance	0	0
Average Recorded Investment	$ 68	$ 1

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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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+ References

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+ References

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+ References

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