Loans and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 45,779	$ 41,877
Provision for loan losses	1,950	2,328
Recoveries	489	1,649
Charge-offs	(2,026)	(1,782)
Ending balance	46,192	44,072
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	11,707	12,644
Provision for loan losses	1,003	847
Recoveries	227	286
Charge-offs	(1,255)	(872)
Ending balance	11,682	12,905
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,101	1,191
Provision for loan losses	(153)	196
Recoveries	6	11
Charge-offs	(8)	(143)
Ending balance	946	1,255
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	26,864	24,375
Provision for loan losses	773	832
Recoveries	52	1,227
Charge-offs	(410)	(335)
Ending balance	27,279	26,099
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	6,107	3,667
Provision for loan losses	327	453
Recoveries	204	125
Charge-offs	(353)	(432)
Ending balance	$ 6,285	$ 3,813

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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Amount of expense related to estimated loss from loan and lease transactions.

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