Derivatives and Hedging Activities (Details) - USD ($)	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Derivative [Line Items]
Gain (loss) on derivative instruments	$ 0	$ 0
Derivative asset, fair value, gross asset	4,554,000		$ 20,895,000
Derivative liability, fair value, gross liability	4,060,000		55,554,000
Interest rate swap agreements
Derivative [Line Items]
Customer derivatives program	925,365,000		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	319,000		0
Borrowings hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	0		31,347,000
Interest rate contracts | Other assets
Derivative [Line Items]
Derivative asset, fair value, gross asset	4,060,000		20,895,000
Interest rate contracts | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	4,060,000		20,895,000
Commercial loan hedges | Other assets
Derivative [Line Items]
Derivative asset, fair value, gross asset	175,000		0
Commercial loan hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value, gross liability	$ 0		$ 3,312,000