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	Mar. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	$ 4,999	$ 5,222
Fair value adjustment for credit impaired loans	(1,996)	(2,119)
Carrying balance of acquired credit impaired loans	3,003	3,103
Construction / Land
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	744	750
One-to-four family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	2,089	2,149
Multi-family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	686	685
Nonresidential real estate and agricultural land
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	1,396	1,523
Commercial
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	38	64
Consumer
Business Acquisition [Line Items]
Outstanding balance of acquired credit impaired loans	$ 46	$ 51