Loans and Allowance for Loan Losses (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended	9 Months Ended				6 Months Ended				6 Months Ended		6 Months Ended
	Jun. 30, 2012 loan standard_deviations	Jun. 30, 2011 loan	Mar. 31, 2011 loan	Jun. 30, 2012 loan standard_deviations	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Commercial and Consumer Federal Reserve Bank	Dec. 31, 2011 Commercial and Consumer Federal Reserve Bank	Jun. 30, 2012 Individual Real Estate-Secured Loans	Jun. 30, 2011 Individual Real Estate-Secured Loans	Jun. 30, 2012 Individual Real Estate-Secured Loans Federal Home Loan Bank Advances	Dec. 31, 2011 Individual Real Estate-Secured Loans Federal Home Loan Bank Advances	Jun. 30, 2012 Commercial Real Estate	Dec. 31, 2011 Commercial Real Estate	Jun. 30, 2011 Agricultural Loans	Dec. 31, 2011 Commerical Agricultural and Municipal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, unearned income	$ 1,437			$ 1,437		$ 2,045
Loans pledged as collateral							11,344	18,005			172,152	216,201
Loan participations purchased during period, held for investment													821		2,138
Transfer of mortgage loans from held-for-sale to loans held for investment									4,199	454
Allowance for loan losses, historical period used for loss rates	5 years				13 years
Standard deviations applied to analysis on estimating loan loss rates	2			2
Adjustment to historical loan loss rate due to environmental factors (as a percentage)														0.10%		0.50%
Adjustment to average loss rate due change in historical period used in calculation (as a percentage)														0.27%
Credit commitments available for construction and land development restructured loans	$ 175			$ 175		$ 356
Loans restructured during the period	0	11	0	0