Loans and Allowance for Loan Losses - Schedule of Non-Accrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 27,175	$ 28,601	$ 18,935
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	7,392	8,761	3,098
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	19	97	197
Real Estate Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	18,473	18,766	14,983
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 1,291	$ 977	$ 657