Loans, Allowance for Credit Losses and Credit Quality - Financing Receivable, Allowance for Credit Loss (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		9 Months Ended
		Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Sep. 30, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		$ 190,560	$ 144,092	$ 189,877	$ 169,984	$ 169,984
Allowance for Loan and Lease Losses, Write-offs		(1,865)	(6,966)	(7,641)	(48,366)	(56,804)	[1]
Allowance for Loan and Lease Loss, Recovery of Bad Debts		954	447	1,913	955
Ending balance	[2]	195,899	144,773	195,899	144,773
Provision for Loan and Lease Losses		6,250	7,200	11,750	22,200
Accounts Receivable, Noncurrent, Accrued Interest, Writeoff		579	224	795	568
Commercial And Industrial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		49,282	37,219	47,976	30,799	30,799
Allowance for Loan and Lease Losses, Write-offs		(538)	(2,845)	(1,008)	(3,012)	(8,813)
Allowance for Loan and Lease Loss, Recovery of Bad Debts		74	52	233	67
Ending balance	[2]	56,880	38,451	56,880	38,451
Provision for Loan and Lease Losses		8,062	4,025	9,679	10,597
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		82,992	61,416	84,916	93,718	93,718
Allowance for Loan and Lease Losses, Write-offs		(146)	(3,348)	(4,370)	(43,344)	(43,412)
Allowance for Loan and Lease Loss, Recovery of Bad Debts		88	1	278	1
Ending balance	[2]	78,879	60,927	78,879	60,927
Provision for Loan and Lease Losses		(4,055)	2,858	(1,945)	10,552
Construction Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		14,212	8,377	14,254	8,166	8,166
Allowance for Loan and Lease Losses, Write-offs		0	0	0	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts		0	0	0	0
Ending balance	[2]	13,871	8,183	13,871	8,183
Provision for Loan and Lease Losses		(341)	(194)	(383)	17
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		29,900	25,469	29,254	25,238	25,238
Allowance for Loan and Lease Losses, Write-offs		0	0	0	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts		0	0	0	0
Ending balance	[2]	31,543	25,414	31,543	25,414
Provision for Loan and Lease Losses		1,643	(55)	2,289	176
Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		13,268	10,846	12,376	11,007	11,007
Allowance for Loan and Lease Losses, Write-offs		(2)	0	(2)	(96)	(96)
Allowance for Loan and Lease Loss, Recovery of Bad Debts		45	49	57	67
Ending balance	[2]	13,562	10,911	13,562	10,911
Provision for Loan and Lease Losses		251	16	1,131	(67)
Consumer - Other [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		906	765	1,101	1,056	$ 1,056
Allowance for Loan and Lease Losses, Write-offs		(1,179)	(773)	(2,261)	(1,914)
Allowance for Loan and Lease Loss, Recovery of Bad Debts		747	345	1,345	820
Ending balance	[2]	1,164	887	1,164	887
Provision for Loan and Lease Losses		$ 690	$ 550	$ 979	$ 925

[1] (2)Loan origination dates in the tables above reflect the original origination date, or the date of a material modification of a previously originated loan.

[2] Balances of accrued interest receivable excluded from amortized cost and the calculation of allowance for credit losses amounted to $68.3 million and $54.5 million as of June 30, 2026 and June 30, 2025, respectively.