Contingencies (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Maximum potential exposure to credit loss in the event of nonperformance	$ 156.1	$ 161.7
Letters of credit, maturity term - maximum	3 years
Collateral held, fair value	$ 52.7
Pending or Threatened Litigation, Stanford Financial Group [Member]
Legal Proceedings [Abstract]
Lawsuits naming entity as defendant, number	2
Pending or Threatened Litigation, Overdraft Fees [Member]
Legal Proceedings [Abstract]
Lawsuits naming entity as defendant, number	2