Accounting for Certain Loans Acquired in a Transfer - Carrying amount of loans included in balance sheet of loans receivable (Details) (Dupont State Bank, Loans Receivable, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	$ 5,222
Fair value adjustment for credit impaired loans	(2,119)
Carrying balance of acquired credit impaired loans	3,103
Residential Real Estate - Construction
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans
Residential Real Estate - One-to-four family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	2,149
Residential Real Estate - Multi-family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	685
Nonresidential real estate and agricultural land
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	1,523
Land and land development
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	750
Commercial
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	64
Consumer and other
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	$ 51