Accounting for Certain Loans Acquired in a Transfer - Carrying amount of loans included in balance sheet of loans receivable (Details) (Loans Receivable, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans	$ 1,873	$ 2,857
Construction/Land
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans	411	337
One-to-four family residential
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans	1,035	1,281
Multi-family residential
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans		500
Nonresidential real estate and agricultural land
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans	403	705
Commercial
Business Acquisition [Line Items]
Carrying balance of acquired credit-impaired loans	14	15
Dupont State Bank
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	2,703	4,398
Fair value adjustment for credit-impaired loans	(830)	(1,541)
Carrying balance of acquired credit-impaired loans	1,873	2,857
Dupont State Bank | Construction/Land
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	682	713
Dupont State Bank | One-to-four family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	1,400	1,812
Dupont State Bank | Multi-family residential
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans		685
Dupont State Bank | Nonresidential real estate and agricultural land
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	568	1,124
Dupont State Bank | Commercial
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	24	26
Dupont State Bank | Consumer and other
Business Acquisition [Line Items]
Outstanding balance of acquired credit-impaired loans	$ 29	$ 38