Loans and Allowance - Corporation's nonaccrual loans (Details 5) (Loans Receivable, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	$ 10,850	$ 9,863
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	413
One-to-four family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	2,687	4,304
Multi-family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	1,104
Nonresidential real estate and agricultural land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	1,678	2,161
Land (not used for agricultural purposes)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	4,385	3,080
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	567	297
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonaccrual loans	$ 16	$ 21