Borrowed Funds (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
FHLB Advances, Fixed Rate	$ 2,010,000		$ 2,020,000
FHLB Advances, Variable Rate	365,000		365,000
Finance Lease, Liability	974
Repayments on borrowings	682,521	$ 1,487,518
Interest rate swaps, notional amount	$ 365,000		$ 365,000
Interest rate swaps, remaining term to maturity	1 year 9 months 18 days		2 years 1 month 6 days
Interest rate swaps, fair value	$ 6,500		$ 13,000
Derivative Asset, balance sheet location	Other assets
Interest rate swaps, amount reclassified from AOCI	$ (1,940)	$ (734)
Interest rate swaps, future amount to be reclassified from AOCI	(5,200)
Interest rate swaps, collateral held	(7,200)		(14,000)
FHLB advances [Member]
FHLB Advances, Amount	2,380,000		2,380,000
Federal Reserve Bank Advances [Member]
BTFP borrowings			$ 500,000
Repayments on borrowings	$ 500,000