Allowance for Loan Losses and Credit Quality Information - Schedule of Allowance for Loan Losses and Loan Balances (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014
Receivables [Abstract]
Accrued troubled debt restructured loans	$ 13.6	$ 11.8

Modifications Recorded Investment Financing Receivable Individually Evaluated for Impairment

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant