Preferred Stock (Additional Information) (Detail) - USD ($)	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2016	Feb. 11, 2016	Aug. 11, 2011
Auction Market Preferred Securities, Stock Series [Line Items]
Weighted Average Dividend Rate	1.00%
Preferred Stock, issued	0	0		17,120
Series A Preferred Stock, total purchase price under Purchase Agreement				$ 17,120,000
Preferred Stock, aggregate liquidation preference				$ 1,000
Tier One Risk Based Capital				$ 10,000,000,000
Preferred Stock Value	$ 0	$ 0
Small Business Jobs Act of 2010
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock Value				$ 30,000,000,000
Redeemable Preferred Stock
Auction Market Preferred Securities, Stock Series [Line Items]
Series A Preferred Stock, total purchase price under Purchase Agreement			$ 17,120,000