Loans and Allowance for Loan Losses Loans and Allowance for Loan Losses - Allowance (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 alternative	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Minimum balance of adversely classified loan in which a detailed analysis is performed									$ 100,000
Number of alternatives for measuring impaired loans receivable									3
Time Period Used Base For Loss Estimations									five-year
Balance, beginning of year				13,249,000				11,776,000	13,249,000	11,776,000	11,120,000
Provision charged to expense	134,000	44,000	128,000	323,000	486,000	975,000	252,000	480,000	629,000	2,193,000	2,647,000
Losses charged off									(537,000)	(1,128,000)	(2,371,000)
Recoveries									341,000	408,000	380,000
Balance, end of period	13,682,000				13,249,000				13,682,000	13,249,000	11,776,000
Individually evaluated for impairment	263,000				604,000				263,000	604,000	511,000
Collectively evaluated for impairment	13,419,000				12,645,000				13,419,000	12,645,000	11,265,000
Ending balance	1,062,406,000				982,804,000				1,062,406,000	982,804,000	911,065,000
Individually evaluated for impairment	3,301,000				5,145,000				3,301,000	5,145,000	6,564,000
Collectively evaluated for impairment	1,059,105,000				977,659,000				1,059,105,000	977,659,000	904,501,000
Unsecured Open-end Loans [Member]
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down									180 days
Other Secured Loans [Member]
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down									120 days
Commercial/Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year				10,646,000				9,301,000	10,646,000	9,301,000	8,791,000
Provision charged to expense									192,000	1,861,000	1,979,000
Losses charged off									(86,000)	(764,000)	(1,586,000)
Recoveries									162,000	248,000	117,000
Balance, end of period	10,914,000				10,646,000				10,914,000	10,646,000	9,301,000
Individually evaluated for impairment	263,000				604,000				263,000	604,000	457,000
Collectively evaluated for impairment	10,651,000				10,042,000				10,651,000	10,042,000	8,844,000
Ending balance	684,552,000				607,062,000				684,552,000	607,062,000	569,717,000
Individually evaluated for impairment	3,301,000				5,145,000				3,301,000	5,145,000	5,334,000
Collectively evaluated for impairment	681,251,000				601,917,000				681,251,000	601,917,000	564,383,000
Agriculture/Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year				533,000				558,000	533,000	558,000	546,000
Provision charged to expense									825,000	(30,000)	(47,000)
Losses charged off									0	0	(12,000)
Recoveries									2,000	5,000	71,000
Balance, end of period	1,360,000				533,000				1,360,000	533,000	558,000
Individually evaluated for impairment	0				0				0	0	54,000
Collectively evaluated for impairment	1,360,000				533,000				1,360,000	533,000	504,000
Ending balance	178,091,000				172,979,000				178,091,000	172,979,000	145,695,000
Individually evaluated for impairment	0				0				0	0	1,230,000
Collectively evaluated for impairment	178,091,000				172,979,000				178,091,000	172,979,000	144,465,000
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year				771,000				726,000	771,000	726,000	636,000
Provision charged to expense									135,000	171,000	580,000
Losses charged off									(140,000)	(141,000)	(524,000)
Recoveries									24,000	15,000	34,000
Balance, end of period	790,000				771,000				790,000	771,000	726,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	790,000				771,000				790,000	771,000	726,000
Ending balance	184,661,000				187,796,000				184,661,000	187,796,000	179,309,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	184,661,000				187,796,000				184,661,000	187,796,000	179,309,000
1-4 Family residential properties
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down									180 days
Consumer loans
Financing Receivable, Impaired [Line Items]
Balance, beginning of year				377,000				403,000	377,000	403,000	378,000
Provision charged to expense									167,000	57,000	116,000
Losses charged off									(311,000)	(223,000)	(249,000)
Recoveries									153,000	140,000	158,000
Balance, end of period	386,000				377,000				386,000	377,000	403,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	386,000				377,000				386,000	377,000	403,000
Ending balance	15,102,000				14,967,000				15,102,000	14,967,000	16,066,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	15,102,000				14,967,000				15,102,000	14,967,000	16,066,000
Unallocated [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year				922,000				788,000	922,000	788,000	769,000
Provision charged to expense									(690,000)	134,000	19,000
Losses charged off									0	0	0
Recoveries									0	0	0
Balance, end of period	232,000				922,000				232,000	922,000	788,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	232,000				922,000				232,000	922,000	788,000
Ending balance	0				0				0	0	278,000
Individually evaluated for impairment	0				0				0	0	0
Collectively evaluated for impairment	$ 0				$ 0				$ 0	$ 0	$ 278,000