Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 3,549,125	$ 2,828,813
30-59 Days Past Due	16,864	14,303
60-89 Days Past Due	8,668	3,657
Loans 90 Days And Accruing	1,350	2,037
Non-Accrual	56,402	53,399
Total Past Due & Non-Accrual	83,284	73,396
Total Loans	3,632,409	2,902,209
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	749,020	607,442
30-59 Days Past Due	2,628	2,628
60-89 Days Past Due	774	144
Loans 90 Days And Accruing		170
Non-Accrual	9,283	12,195
Total Past Due & Non-Accrual	12,685	15,137
Total Loans	761,705	622,579
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	114,305	112,527
30-59 Days Past Due	13
Non-Accrual	30
Total Past Due & Non-Accrual	43
Total Loans	114,348	112,527
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	171,046	93,426
30-59 Days Past Due	1,058	399
Non-Accrual	4,978	4,814
Total Past Due & Non-Accrual	6,036	5,213
Total Loans	177,082	98,639
Commercial and farmland
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,573,403	1,238,907
30-59 Days Past Due	3,807	3,276
60-89 Days Past Due	5,801	1,822
Loans 90 Days And Accruing	703	65
Non-Accrual	28,095	22,612
Total Past Due & Non-Accrual	38,406	27,775
Total Loans	1,611,809	1,266,682
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	595,192	453,743
30-59 Days Past Due	7,156	5,734
60-89 Days Past Due	1,475	1,338
Loans 90 Days And Accruing	494	1,246
Non-Accrual	12,068	11,476
Total Past Due & Non-Accrual	21,193	19,794
Total Loans	616,385	473,537
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	251,188	199,063
30-59 Days Past Due	1,652	1,467
60-89 Days Past Due	563	323
Loans 90 Days And Accruing	153	556
Non-Accrual	1,667	1,997
Total Past Due & Non-Accrual	4,035	4,343
Total Loans	255,223	203,406
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	69,061	74,919
30-59 Days Past Due	550	799
60-89 Days Past Due	55	30
Non-Accrual	117
Total Past Due & Non-Accrual	722	829
Total Loans	69,783	75,748
Finance Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,545	2,289
Non-Accrual		301
Total Past Due & Non-Accrual		301
Total Loans	1,545	2,590
Other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	24,365	46,497
Non-Accrual	164	4
Total Past Due & Non-Accrual	164	4
Total Loans	$ 24,529	$ 46,501