Loans and Allowance for Loan Losses (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) alternative	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	$ 1,722,000	$ 113,000	$ 2,826,000
Gross loans				$ 1,804,512,000	$ 1,836,251,000
Loans Receivable Held-for-sale, Amount				1,578,000	1,175,000
loans and leases receivable gross excluding loans held for sale				1,802,934,000	1,835,076,000
Less [Abstract]
Net deferred loan fees, premiums and discounts				8,850,000	10,259,000
Allowance for loan losses	16,753,000	14,576,000	14,576,000	17,846,000	16,753,000	$ 14,736,000
Net loans				1,776,238,000	1,808,064,000
Increase (Decrease) in loans receivable	(31,800,000)
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	$ 16,753,000	14,576,000	14,576,000
Provision for Loan and Lease Losses	1,722,000	113,000
Losses charged off	(763,000)	(237,000)	(1,675,000)
Recoveries	134,000	284,000	1,026,000
Balance, end of period	$ 17,846,000	14,736,000	16,753,000
Ending Balance [Abstract]
Individually evaluated for impairment				1,070,000	858,000	298,000
Collectively evaluated for impairment				16,751,000	15,881,000	14,438,000
Ending Balance [Abstract]
Individually evaluated for impairment				16,223,000	5,266,000	1,631,000
Collectively evaluated for impairment				1,771,471,000	1,812,640,000	1,275,274,000
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				1,795,662,000	1,825,992,000	1,276,905,000
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				58,489,000	49,366,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				58,303,000	49,104,000
Agricultural real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				123,160,000	126,216,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				123,061,000	126,108,000
1-4 Family residential properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				321,238,000	328,119,000
Ending Balance [Abstract]
Period When Loans are Charged-down	180 days
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				319,714,000	326,415,000
Multifamily residential properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				74,882,000	83,478,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				74,714,000	83,200,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				627,415,000	633,694,000
Loans Receivable Additional Information [Abstract]
Debt coverage ratio	1.20x
Amortization period of loans	twenty years
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				624,372,000	630,135,000
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				1,205,184,000	1,220,873,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				1,200,164,000	1,214,962,000
Agricultural loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				76,782,000	86,735,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				76,757,000	86,685,000
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				403,135,000	412,637,000
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
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				400,810,000	409,033,000
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	$ 50,000	123,000	501,000
Gross loans				36,070,000	38,404,000
Less [Abstract]
Allowance for loan losses	693,000	642,000	642,000	751,000	693,000	710,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	693,000	642,000	642,000
Losses charged off	(102,000)	(113,000)	(664,000)
Recoveries	110,000	58,000	214,000
Balance, end of period	751,000	710,000	693,000
Ending Balance [Abstract]
Individually evaluated for impairment				1,000	0	0
Collectively evaluated for impairment				750,000	693,000	710,000
Ending Balance [Abstract]
Individually evaluated for impairment				301,000	213,000	0
Collectively evaluated for impairment				38,451,000	41,644,000	42,108,000
Loans Receivable, Net				38,752,000	41,857,000	42,108,000
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				34,962,000	38,028,000
All other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				83,341,000	77,602,000
Ending Balance [Abstract]
Loans and Leases Receivable, Including Held for Sale, Net of Deferred Income				82,969,000	77,284,000
Agricultural and Farm Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				199,900,000	213,000,000
Less [Abstract]
Increase (Decrease) in loans receivable	$ (13,100,000)
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				162,200,000	171,300,000
Less [Abstract]
Increase (Decrease) in loans receivable	$ (9,100,000)
Motels and Hotels Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				112,900,000
Non-residential Buildings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				141,700,000
Residential Buildings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				131,400,000
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)	$ 1,466,000	225,000	1,467,000
Less [Abstract]
Allowance for loan losses	12,901,000	11,379,000	11,379,000	13,771,000	12,901,000	11,789,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	12,901,000	11,379,000	11,379,000
Losses charged off	(612,000)	(40,000)	(747,000)
Recoveries	16,000	225,000	802,000
Balance, end of period	13,771,000	11,789,000	12,901,000
Ending Balance [Abstract]
Individually evaluated for impairment				316,000	192,000	298,000
Collectively evaluated for impairment				13,455,000	12,695,000	11,491,000
Ending Balance [Abstract]
Individually evaluated for impairment				10,656,000	1,956,000	1,201,000
Collectively evaluated for impairment				1,190,272,000	1,199,003,000	820,655,000
Loans Receivable, Net				1,204,748,000	1,204,799,000	821,856,000
Agricultural/ Agricultural Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	69,000	(68,000)	933,000
Less [Abstract]
Allowance for loan losses	2,249,000	1,337,000	1,337,000	2,319,000	2,249,000	1,270,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	2,249,000	1,337,000	1,337,000
Losses charged off	0	0	(30,000)
Recoveries	1,000	1,000	9,000
Balance, end of period	2,319,000	1,270,000	2,249,000
Ending Balance [Abstract]
Individually evaluated for impairment				709,000	660,000	0
Collectively evaluated for impairment				1,610,000	1,589,000	1,270,000
Ending Balance [Abstract]
Individually evaluated for impairment				1,173,000	1,345,000	430,000
Collectively evaluated for impairment				198,588,000	211,168,000	185,836,000
Loans Receivable, Net				199,761,000	212,513,000	186,266,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	146,000	16,000	113,000
Less [Abstract]
Allowance for loan losses	$ 874,000	994,000	994,000	978,000	874,000	926,000
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	$ 874,000	994,000	994,000
Losses charged off	(49,000)	(84,000)	(234,000)
Recoveries	7,000	0	1,000
Balance, end of period	978,000	926,000	874,000
Ending Balance [Abstract]
Individually evaluated for impairment				44,000	6,000	0
Collectively evaluated for impairment				909,000	868,000	926,000
Ending Balance [Abstract]
Individually evaluated for impairment				4,093,000	1,752,000	0
Collectively evaluated for impairment				344,160,000	360,825,000	226,675,000
Loans Receivable, Net				352,401,000	366,823,000	226,675,000
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	(9,000)	(183,000)	(188,000)
Less [Abstract]
Allowance for loan losses	36,000	224,000	224,000	27,000	36,000	41,000
Allowance for Loan Losses [Abstract]
Balance, beginning of period	36,000	224,000	224,000
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	$ 27,000	$ 41,000	$ 36,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				27,000	36,000	41,000
Ending Balance [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				0	0	0
Loans Receivable, Net				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member]
Less [Abstract]
Net loans				7,943,000	8,072,000
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				25,000	14,000	0
Ending Balance [Abstract]
Financing Receivable, Net				7,968,000	8,086,000	0
Receivables Acquired with Deteriorated Credit Quality [Member] | 1-4 Family residential properties
Ending Balance [Abstract]
Financing Receivable, Net				740,000	827,000
Receivables Acquired with Deteriorated Credit Quality [Member] | Multifamily residential properties
Ending Balance [Abstract]
Financing Receivable, Net				3,408,000	3,419,000
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial and industrial loans
Ending Balance [Abstract]
Financing Receivable, Net				20,000	24,000
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer loans
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				0	0	0
Ending Balance [Abstract]
Financing Receivable, Net				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial/ Commercial Real Estate
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				0	14,000	0
Ending Balance [Abstract]
Financing Receivable, Net				3,820,000	3,840,000	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Agricultural/ Agricultural Real Estate
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				0	0	0
Ending Balance [Abstract]
Financing Receivable, Net				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential Real Estate
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				25,000	0	0
Ending Balance [Abstract]
Financing Receivable, Net				4,148,000	4,246,000	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Unallocated
Ending Balance [Abstract]
Financing Receivable, Allowance for Credit Losses				0	0	0
Ending Balance [Abstract]
Financing Receivable, Net				$ 0	$ 0	$ 0