Loans and allowance for loan losses (Details Textual)	6 Months Ended
Jun. 30, 2015
Loans Insured or Guaranteed by US Government Authorities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Description	Loans greater than 90 days past due are student loans that are guaranteed by the Department of Education which covers approximately 98% of the principal and interest. Accordingly, these loans will not be placed on nonaccrual status

Describes the major category and subcategories of loans held, any unusual risk concentration relating thereto, and the related loans receivable carrying amounts as of the balance sheet date. Such descriptions may include information pertaining to: (i) type of borrower, (ii) purpose of the loan, (iii) loan maturity, (iv) credit and other risk associated with the loan, and (v) other terms of importance (secured or unsecured, variable or fixed interest).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5066-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a),(b))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_LoansAndLeasesReceivableDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration