Loans and reserve for credit losses (Details 10) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 unit	Mar. 31, 2012 unit
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2	9
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 3,500	$ 7,364
Commercial real estate [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	3,500	2,264
Construction [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	160
Residential real estate [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	40
Commercial and industrial loans [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	4,858
Consumer Loans [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	4
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 42