Loans and Allowance for Loan Losses (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) alternative	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan and Lease Losses	$ 113,000	$ 265,000
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	113,000	265,000	$ 1,318,000
Gross loans				$ 1,277,705,000	$ 1,283,709,000
Less [Abstract]
Net deferred loan fees, premiums and discounts				2,538,000	2,788,000
Allowance for loan losses	14,576,000	13,682,000	13,682,000	14,736,000	14,576,000	$ 14,106,000
Net loans				1,260,431,000	1,266,345,000
Loans held for sale				1,738,000	968,000
Impaired Loans [Abstract]
Minimum value of loans individually measured for impairment	$ 250,000
Number of alternatives for measuring impaired loans receivable | alternative	3
Allowance for Loan Losses [Abstract]
Balance, beginning of period	$ 14,576,000	13,682,000	13,682,000
Losses charged off	(237,000)	(90,000)	(906,000)
Recoveries	284,000	249,000	482,000
Balance, end of period	$ 14,736,000	14,106,000	14,576,000
Ending Balance [Abstract]
Individually evaluated for impairment				298,000	134,000	625,000
Collectively evaluated for impairment				14,438,000	14,442,000	13,481,000
Loans [Abstract]
Ending balance				1,276,905,000	1,281,889,000	1,054,156,000
Ending Balance [Abstract]
Individually evaluated for impairment				1,631,000	1,174,000	3,392,000
Collectively evaluated for impairment				1,275,274,000	1,280,715,000	1,050,764,000
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				29,461,000	39,232,000
Agricultural real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				119,508,000	122,579,000
1-4 Family residential properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				225,159,000	231,383,000
Ending Balance [Abstract]
Period When Loans are Charged-down	180 days
Multifamily residential properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				47,359,000	45,765,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				438,607,000	409,487,000
Loans Receivable Additional Information [Abstract]
Debt coverage ratio	1.20x
Amortization period of loans	twenty years
Commercial real estate | Minimum [Member]
Loans Receivable Additional Information [Abstract]
Maximum Loan-to-value Ratio (in hundredths)	65.00%
Commercial real estate | Maximum [Member]
Loans Receivable Additional Information [Abstract]
Maximum Loan-to-value Ratio (in hundredths)	80.00%
Loans secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				860,094,000	848,446,000
Agricultural loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				67,239,000	75,998,000
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				298,588,000	305,851,000
Loans Receivable Additional Information [Abstract]
Maximum Loan-to-value Ratio (in hundredths)	80.00%
Amortization period of loans	seven years
Loans Receivable, Time Period	one year
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	$ 123,000	4,000	633,000
Gross loans				40,084,000	42,097,000
Less [Abstract]
Allowance for loan losses	642,000	386,000	386,000	710,000	642,000	386,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	642,000	386,000	386,000
Losses charged off	(113,000)	(56,000)	(553,000)
Recoveries	58,000	52,000	176,000
Balance, end of period	710,000	386,000	642,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				710,000	642,000	386,000
Loans [Abstract]
Ending balance				42,108,000	43,739,000	15,355,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				42,108,000	43,739,000	15,355,000
All other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				11,700,000	11,317,000
Agricultural and Farm Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				186,700,000	198,600,000
Less [Abstract]
Decrease in loans receivable	$ (11,900,000)
Loans Receivable Additional Information [Abstract]
Maximum Loan-to-value Ratio (in hundredths)	65.00%
Amortization period of loans	twenty five years
Loans Receivable, Time Period	one year
Other Grain Farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				151,800,000	161,500,000
Less [Abstract]
Decrease in loans receivable	$ (9,700,000)
Motels and Hotels Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				63,600,000
Non-residential Buildings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				111,700,000
Residential Buildings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				65,300,000
Unsecured Open-end Loans [Member]
Ending Balance [Abstract]
Period When Loans are Charged-down	180 days
Other Secured Loans [Member]
Ending Balance [Abstract]
Period When Loans are Charged-down	120 days
Commercial/ Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	$ 225,000	358,000	451,000
Less [Abstract]
Allowance for loan losses	11,379,000	10,914,000	10,914,000	11,789,000	11,379,000	11,459,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	11,379,000	10,914,000	10,914,000
Losses charged off	(40,000)	(9,000)	(289,000)
Recoveries	225,000	196,000	303,000
Balance, end of period	11,789,000	11,459,000	11,379,000
Ending Balance [Abstract]
Individually evaluated for impairment				298,000	134,000	625,000
Collectively evaluated for impairment				11,491,000	11,245,000	10,834,000
Loans [Abstract]
Ending balance				821,856,000	807,736,000	694,836,000
Ending Balance [Abstract]
Individually evaluated for impairment				1,201,000	744,000	3,392,000
Collectively evaluated for impairment				820,655,000	806,992,000	691,444,000
Agricultural/ Agricultural Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	(68,000)	(69,000)	(25,000)
Less [Abstract]
Allowance for loan losses	1,337,000	1,360,000	1,360,000	1,270,000	1,337,000	1,291,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	1,337,000	1,360,000	1,360,000
Losses charged off	0	0	0
Recoveries	1,000	0	2,000
Balance, end of period	1,270,000	1,291,000	1,337,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				1,270,000	1,337,000	1,291,000
Loans [Abstract]
Ending balance				186,266,000	198,066,000	165,927,000
Ending Balance [Abstract]
Individually evaluated for impairment				430,000	430,000	0
Collectively evaluated for impairment				185,836,000	197,636,000	165,927,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	16,000	(13,000)	267,000
Less [Abstract]
Allowance for loan losses	$ 994,000	790,000	790,000	926,000	994,000	753,000
Loans Receivable Additional Information [Abstract]
Maximum Loan-to-value Ratio (in hundredths)	80.00%
Amortization period of loans	twenty five years
Balloon period	five years
Allowance for Loan Losses [Abstract]
Balance, beginning of period	$ 994,000	790,000	790,000
Losses charged off	(84,000)	(25,000)	(64,000)
Recoveries	0	1,000	1,000
Balance, end of period	926,000	753,000	994,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				926,000	994,000	753,000
Loans [Abstract]
Ending balance				226,675,000	232,348,000	178,038,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				226,675,000	232,348,000	178,038,000
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	(183,000)	(15,000)	(8,000)
Less [Abstract]
Allowance for loan losses	224,000	232,000	232,000	41,000	224,000	217,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	224,000	232,000	232,000
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	$ 41,000	$ 217,000	$ 224,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				41,000	224,000	217,000
Loans [Abstract]
Ending balance				0	0	0
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				$ 0	$ 0	$ 0