Borrowed Funds (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Debt Disclosure [Abstract]
Interest rate swaps, notional amount	$ 640,000,000.0		$ 640,000,000
FHLB advances, variable rate	$ 640,000,000.0		$ 640,000,000
Interest rate swaps, remaining term to maturity	4 years 2 months 12 days		4 years 6 months
Interest rate swaps, fair value	$ (25,900,000)		$ (33,100,000)
Interest rate swaps, amount reclassified from AOCI	709,000	$ 151,000
Interest rate swaps, amount of hedge ineffectiveness recognized	0
Interest rate swaps, future amount to be reclassified from AOCI	5,900,000
Interest rate swaps, collateral posted	$ 26,600,000		$ 33,300,000