Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Segment of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	$ 998	$ 806
60-89 Days Past Due	256	2
Greater Than 90 Days	54	633
Total Past Due	1,308	1,441
Current	596,531	574,672
Total Financing Receivables	597,839	576,113	501,074
Recorded Investment > 90 Days and Accruing	0	0	0
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	970	778
60-89 Days Past Due	256
Greater Than 90 Days	54	234
Total Past Due	1,280	1,012
Current	94,583	91,426
Total Financing Receivables	95,863	92,438	77,948
Recorded Investment > 90 Days and Accruing	0	0
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	47,745	44,301
Total Financing Receivables	47,745	44,301	35,746
Recorded Investment > 90 Days and Accruing	0	0
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	14
Total Past Due	14
Current	63,379	65,449
Total Financing Receivables	63,393	65,449	55,331
Recorded Investment > 90 Days and Accruing	0	0
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	12
Greater Than 90 Days		373
Total Past Due	12	373
Current	265,890	248,520
Total Financing Receivables	265,902	248,893	215,246
Recorded Investment > 90 Days and Accruing	0	0
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater Than 90 Days		26
Total Past Due		26
Current	102,455	103,830
Total Financing Receivables	102,455	103,856	97,080
Recorded Investment > 90 Days and Accruing	0	0
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	2	28
60-89 Days Past Due		2
Total Past Due	2	30
Current	22,479	21,146
Total Financing Receivables	22,481	21,176	19,723
Recorded Investment > 90 Days and Accruing	$ 0	$ 0