Loans and reserve for credit losses (Details 10) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1	5
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 193	$ 526
Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2	23
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	196	9,756
Commercial real estate [Member] | Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Commercial real estate [Member] | Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	573
Construction [Member] | Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Construction [Member] | Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Residential Real Estate [Member] | Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	302
Residential Real Estate [Member] | Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	3
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	636
Commercial and industrial loans [Member] | Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1	3
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	193	224
Commercial and industrial loans [Member] | Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1	12
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	193	8,476
Consumer Loan [Member] | Three Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Consumer Loan [Member] | Nine Months Ended [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1	7
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 3	$ 71