Derivatives and Hedging Activities (Details) - USD ($)	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Derivative [Line Items]
Gain (loss) on derivative instruments	$ 0	$ 0
Derivative asset, fair value, gross asset	1,342,000		$ 20,895,000
Derivative liability, fair value, gross liability	4,032,000		55,554,000
Interest rate swap agreements
Derivative [Line Items]
Customer derivatives program	984,549,000		840,935,000
Notional amount	700,000,000	$ 700,000,000
Commercial loan interest rate swap
Derivative [Line Items]
Notional amount	52,936,000		54,155,000
Borrowings hedges | Other assets
Derivative [Line Items]
Derivative asset, fair value, gross asset	0		0
Borrowings hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	2,536,000		31,347,000
Interest rate contracts | Other assets
Derivative [Line Items]
Derivative asset, fair value, gross asset	1,342,000		20,895,000
Interest rate contracts | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	1,342,000		20,895,000
Commercial loan hedges | Other assets
Derivative [Line Items]
Derivative asset, fair value, gross asset	0		0
Commercial loan hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	$ 154,000		$ 3,312,000