Loans and Allowance for Loan Losses - Schedule of Impaired Loans and Related Allowance (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid Contractual Principal Balance	$ 46,207	$ 23,826	$ 35,030
Recorded Investment With No Allowance	8,784	3,551	6,546
Recorded Investment With Allowance	30,120	13,303	22,055
Total Recorded Investment	38,904	16,854	28,601
Related Allowance	7,102	3,866	5,071
Year Average Recorded Investment	38,996	18,387	21,735
Three-month Average Recorded Investment	39,855	16,877
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid Contractual Principal Balance	19,571	4,168	10,056
Recorded Investment With No Allowance	1,103	263	608
Recorded Investment With Allowance	16,151	3,343	8,153
Total Recorded Investment	17,254	3,606	8,761
Related Allowance	4,144	1,168	2,030
Year Average Recorded Investment	16,970	3,717	5,812
Three-month Average Recorded Investment	17,319	3,298
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid Contractual Principal Balance	20	163	97
Recorded Investment With Allowance	20	118	97
Total Recorded Investment	20	118	97
Related Allowance	20	87	70
Year Average Recorded Investment	22	148	48
Three-month Average Recorded Investment	21	136
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid Contractual Principal Balance	25,241	18,711	23,710
Recorded Investment With No Allowance	7,427	2,921	5,314
Recorded Investment With Allowance	13,008	9,649	13,452
Total Recorded Investment	20,435	12,570	18,766
Related Allowance	2,565	2,506	2,827
Year Average Recorded Investment	20,856	13,817	15,211
Three-month Average Recorded Investment	21,227	12,876
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid Contractual Principal Balance	1,375	784	1,167
Recorded Investment With No Allowance	254	367	624
Recorded Investment With Allowance	941	193	353
Total Recorded Investment	1,195	560	977
Related Allowance	373	105	144
Year Average Recorded Investment	1,148	705	$ 664
Three-month Average Recorded Investment	$ 1,288	$ 567

Average recorded investment in impaired loans.

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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=66008989&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=66008989&loc=d3e5258-111524

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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 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524

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Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

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Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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