Loans and Allowance - Composition of Impaired Loans by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 189,779	$ 109,594	$ 98,922
Recorded Investment	114,253	67,333	59,835
Average Recorded Investment	119,561	76,517	69,330
Interest Income Recognized	2,048	1,498	1,241
Unpaid Principal Balance	6,121	12,918	24,234
Recorded Investment	5,502	11,846	19,940
Related Allowance	1,583	4,243	7,596
Average Recorded Investment	5,607	12,097	21,462
Interest Income Recognized	18	203	321
Impaired Financing Receivable, Unpaid Principal Balance	195,900	122,512	123,156
Impaired Financing Receivable, Recorded Investment	119,755	79,179	79,775
Average Recorded Investment	125,168	88,614	90,792
Interest Income Recognized	2,066	1,701	1,562
Commercial and industrial loans
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	35,066	28,532	23,364
Recorded Investment	16,371	11,730	10,116
Average Recorded Investment	19,209	15,089	13,399
Interest Income Recognized	192	124	615
Unpaid Principal Balance	1,390	4,415	8,691
Recorded Investment	1,216	4,155	8,104
Related Allowance	683	1,628	4,142
Average Recorded Investment	1,240	4,225	8,196
Interest Income Recognized	9	33	174
Agriculture Production financing and other loans to farmers
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	32
Recorded Investment	30
Average Recorded Investment	32
Construction
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	16,109	9,787	14,301
Recorded Investment	10,625	5,164	7,701
Average Recorded Investment	11,621	6,471	8,836
Interest Income Recognized	117	66
Unpaid Principal Balance		1,202	961
Recorded Investment		1,058	961
Related Allowance		105	321
Average Recorded Investment		1,175	961
Commercial and farmland
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	128,073	58,173	49,242
Recorded Investment	83,033	43,204	34,571
Average Recorded Investment	84,057	46,788	39,032
Interest Income Recognized	1,663	1,211	591
Unpaid Principal Balance	4,657	5,579	12,115
Recorded Investment	4,215	5,182	8,748
Related Allowance	894	2,460	2,183
Average Recorded Investment	4,291	5,239	10,028
Interest Income Recognized	9	95	140
Residential
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	6,746	8,820	7,491
Recorded Investment	3,910	6,215	6,185
Average Recorded Investment	4,236	7,129	6,539
Interest Income Recognized	75	83	20
Unpaid Principal Balance	74	1,722	1,888
Recorded Investment	71	1,451	1,575
Related Allowance	6	50	391
Average Recorded Investment	76	1,458	1,687
Interest Income Recognized		75	7
Home Equity
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	3,299	4,199	4,425
Recorded Investment	112	1,006	1,241
Average Recorded Investment	225	1,022	1,500
Interest Income Recognized		13	15
Other loans
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	454	83	99
Recorded Investment	172	14	21
Average Recorded Investment	181	18	24
Interest Income Recognized	1	1
Unpaid Principal Balance			579
Recorded Investment			552
Related Allowance			559
Average Recorded Investment			$ 590

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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=28368275&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=28368275&loc=d3e5258-111524

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+ 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=28368275&loc=SL6953550-111524

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