Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,632,409	$ 2,902,209
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	761,705	622,579
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	114,348	112,527
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	177,082	98,639
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,611,809	1,266,682
Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	616,385	473,537
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	255,223	203,406
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	69,783	75,748
Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans	1,545	2,590
Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	24,529	46,501
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,635,448	2,107,317
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	708,835	559,852
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	114,318	112,209
Commercial Pass | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	162,976	85,728
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,473,714	1,148,561
Commercial Pass | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	143,657	145,402
Commercial Pass | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	6,194	9,092
Commercial Pass | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans	1,420
Commercial Pass | Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	24,334	46,473
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	72,407	69,815
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	11,332	23,678
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans		224
Commercial Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,132	1,384
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	57,676	38,199
Commercial Special Mention | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,232	5,437
Commercial Special Mention | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	35	893
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	146,254	140,553
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	41,013	34,460
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	30	94
Commercial Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	12,029	11,356
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	80,184	79,078
Commercial Substandard | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	11,494	13,880
Commercial Substandard | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,184	1,657
Commercial Substandard | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans	125
Commercial Substandard | Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	195	28
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	661	6,064
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	525	4,589
Commercial Doubtful | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans		553
Commercial Doubtful | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	136	922
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	764,261	569,372
Consumer Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	448,494	301,614
Consumer Performing | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	246,101	189,721
Consumer Performing | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	69,666	75,748
Consumer Performing | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans		2,289
Consumer Non Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	13,378	9,088
Consumer Non Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	945	171
Consumer Non Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	235	291
Consumer Non Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	10,372	6,282
Consumer Non Performing | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,709	2,043
Consumer Non Performing | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	117
Consumer Non Performing | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 301