Fair Value Measurement - Summary of Additional Quantitative Information about Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Estimate	$ 33,566	$ 36,497
Unobservable Input	Appraisal adjustments
Fair value input appraisal adjustments	23.00%	23.00%
Impaired Loans [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	0.00%	0.00%
Impaired Loans [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	30.00%	35.00%
Foreclosed Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Estimate	$ 2,479	$ 2,759
Unobservable Input	Appraisal adjustments
Fair value input appraisal adjustments	21.30%	21.20%
Foreclosed Real Estate Owned [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	20.00%	19.00%
Foreclosed Real Estate Owned [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	40.00%	35.00%
Appraisal of Collateral [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation Techniques	Appraisal of collateral
Appraisal of Collateral [Member] | Foreclosed Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation Techniques	Appraisal of collateral