Derivatives and Hedging Activities (Details) - USD ($)	9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017
Derivative [Line Items]
Gain (loss) on derivative instruments	$ 0	$ 0
Asset Derivatives, Fair Value	32,339,000		$ 1,139,000
Liability Derivatives, Fair Value	10,141,000		3,006,000
Interest rate swap agreements
Derivative [Line Items]
Customer derivatives program	781,626,000		1,035,573,000
Notional amount	700,000,000	$ 700,000,000
Commercial loan interest rate swap
Derivative [Line Items]
Notional amount	97,927,000		52,936,000
Interest rate contracts | Other assets
Derivative [Line Items]
Asset Derivatives, Fair Value	10,141,000		1,139,000
Interest rate contracts | Other liabilities
Derivative [Line Items]
Liability Derivatives, Fair Value	10,141,000		1,139,000
Commercial loan hedges | Other assets
Derivative [Line Items]
Asset Derivatives, Fair Value	3,005,000		0
Commercial loan hedges | Other liabilities
Derivative [Line Items]
Liability Derivatives, Fair Value	0		174,000
Borrowings hedges | Other assets
Derivative [Line Items]
Asset Derivatives, Fair Value	19,193,000		0
Borrowings hedges | Other liabilities
Derivative [Line Items]
Liability Derivatives, Fair Value	$ 0		$ 1,693,000