Trading assets and liabilities (Details Textual) (Sovereign and Corporate Bonds [Member], USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Sovereign and Corporate Bonds [Member]
Secured Debt, Repurchase Agreements	$ 1,300,000	$ 19,000,000
Net gain (loss) from trading	$ 100,000	$ 700,000	$ 100,000

The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

Name:	us-gaap_NetRealizedOrUnrealizedGainLossOnTradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration