Loans - Analysis of Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	$ 6,112	$ 5,357	$ 5,357
Charge Offs	(92)	(366)	(778)
Recoveries	50	69	298
Provision (Credit)	114	428
Other Non-interest expense related to unfunded	(5)	17
Ending Balance	6,179	5,505	6,112
Ending balance: individually evaluated for impairment	428	261
Ending balance: collectively evaluated for impairment	5,751	5,244
Ending balance: loans acquired with deteriorated credit quality	1	2
FINANCING RECEIVABLES:
Ending balance	614,709	582,872	621,926
Ending balance: individually evaluated for impairment	2,243	2,059
Ending balance: collectively evaluated for impairment	612,466	580,813
Ending balance: loans acquired with deteriorated credit quality	520	536
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	537	257	257
Charge Offs		(64)
Recoveries	2	10
Provision (Credit)	(42)	199
Ending Balance	497	402
Ending balance: individually evaluated for impairment	35	44
Ending balance: collectively evaluated for impairment	462	358
Ending balance: loans acquired with deteriorated credit quality	1	2
FINANCING RECEIVABLES:
Ending balance	97,019	91,368	97,550
Ending balance: individually evaluated for impairment	253	181
Ending balance: collectively evaluated for impairment	96,766	91,187
Ending balance: loans acquired with deteriorated credit quality	520	536
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	184			131
Provision (Credit)	3
Ending Balance	187	131		131
Ending balance: collectively evaluated for impairment	187	131
FINANCING RECEIVABLES:
Ending balance	51,396	49,629	50,895
Ending balance: individually evaluated for impairment		141
Ending balance: collectively evaluated for impairment	51,396	49,488
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	547	326	326
Recoveries	1	1
Provision (Credit)	(24)	(3)
Ending Balance	524	324
Ending balance: individually evaluated for impairment	24
Ending balance: collectively evaluated for impairment	500	324
FINANCING RECEIVABLES:
Ending balance	71,571	64,859	74,611
Ending balance: individually evaluated for impairment	24
Ending balance: collectively evaluated for impairment	71,547	64,859
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	2,367	2,107	2,107
Charge Offs		(201)
Recoveries	1	2
Provision (Credit)	(156)	50
Ending Balance	2,212	1,958
Ending balance: individually evaluated for impairment	131	107
Ending balance: collectively evaluated for impairment	2,081	1,851
FINANCING RECEIVABLES:
Ending balance	271,201	261,634	270,188
Ending balance: individually evaluated for impairment	1,139	1,385
Ending balance: collectively evaluated for impairment	270,062	260,249
Commercial and Industrial [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	1,421	1,359	1,359
Recoveries	5	5
Provision (Credit)	(7)	(34)
Ending Balance	1,419	1,330
Ending balance: individually evaluated for impairment	238	110
Ending balance: collectively evaluated for impairment	1,181	1,220
FINANCING RECEIVABLES:
Ending balance	99,895	94,358	104,824
Ending balance: individually evaluated for impairment	827	352
Ending balance: collectively evaluated for impairment	99,068	94,006
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	323	292	292
Charge Offs	(92)	(101)
Recoveries	41	51
Provision (Credit)	12	28
Ending Balance	284	270
Ending balance: collectively evaluated for impairment	284	270
FINANCING RECEIVABLES:
Ending balance	23,627	21,024	23,858
Ending balance: collectively evaluated for impairment	23,627	21,024
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	207	163	163
Other Non-interest expense related to unfunded	(5)	17
Ending Balance	202	180
Ending balance: collectively evaluated for impairment	202	180
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	526	722	722
Provision (Credit)	328	188
Ending Balance	854	910
Ending balance: collectively evaluated for impairment	$ 854	$ 910

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