Loans and Allowance for Loan Losses Loans and Allowance for Loan Losses - Allowance (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 alternative	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Impaired [Line Items]
Minimum balance of adversely classified loan in which a detailed analysis is performed	$ 100
Number of alternatives for measuring impaired loans receivable	3
Time Period Used Base For Loss Estimations	five-year
Balance, beginning of year	11,120	10,393	9,462
Provision charged to expense	2,647	3,101	3,737
Losses charged off	(2,371)	(3,760)	(3,122)
Recoveries	380	1,386	316
Balance, end of period	11,776	11,120	10,393
Individually evaluated for impairment	511	575	1,086
Collectively evaluated for impairment	11,265	10,545	9,307
Ending balance	911,065	860,074	804,581
Individually evaluated for impairment	6,564	5,868	8,484
Collectively evaluated for impairment	904,501	854,206	796,097
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	8,791	8,307	7,428
Provision charged to expense	1,979	2,309	3,473
Losses charged off	(1,586)	(3,077)	(2,770)
Recoveries	117	1,252	176
Balance, end of period	9,301	8,791	8,307
Individually evaluated for impairment	457	575	1,086
Collectively evaluated for impairment	8,844	8,216	7,221
Ending balance	569,717	505,693	465,390
Individually evaluated for impairment	5,334	4,719	7,332
Collectively evaluated for impairment	564,383	500,974	458,058
Agriculture/Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	546	404	315
Provision charged to expense	(47)	205	89
Losses charged off	(12)	(66)	(3)
Recoveries	71	3	3
Balance, end of period	558	546	404
Individually evaluated for impairment	54	0	0
Collectively evaluated for impairment	504	546	404
Ending balance	145,695	130,595	118,973
Individually evaluated for impairment	1,230	1,149	1,152
Collectively evaluated for impairment	144,465	129,446	117,821
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	636	440	488
Provision charged to expense	580	546	(118)
Losses charged off	(524)	(363)	(65)
Recoveries	34	13	135
Balance, end of period	726	636	440
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	726	636	440
Ending balance	179,309	185,151	183,000
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	179,309	185,151	183,000
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	378	392	410
Provision charged to expense	116	122	264
Losses charged off	(249)	(254)	(284)
Recoveries	158	118	2
Balance, end of period	403	378	392
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	403	378	392
Ending balance	16,066	16,270	20,486
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	16,066	16,270	20,486
Unallocated [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	769	850	821
Provision charged to expense	19	(81)	29
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	788	769	850
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	788	769	850
Ending balance	278	22,365	16,732
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	$ 278	$ 22,365	$ 16,732