Loans and Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Total	$ 7,981,007	$ 7,742,958
Nonaccrual	49,618	27,937	$ 22,947
Current
Financing Receivable, Past Due [Line Items]
Total	7,897,242	7,703,543
Total Past Due Loans
Financing Receivable, Past Due [Line Items]
Total	83,765	39,415
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	30,157	5,431
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	3,990	6,047
Commercial loans \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	2,950,110	2,708,531
Nonaccrual	25,648	3,228	6,320
Commercial loans \| Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	1,275,985	1,351,637
Nonaccrual	8,979	11,173	878
Commercial loans \| Commercial construction
Financing Receivable, Past Due [Line Items]
Total	307,012	341,266
Nonaccrual	869	0	4,960
Commercial loans \| Business banking
Financing Receivable, Past Due [Line Items]
Total	1,316,346	1,303,258
Nonaccrual	4,146	2,988	4,147
Commercial loans \| Current \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	2,915,311	2,705,303
Commercial loans \| Current \| Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	1,251,241	1,338,053
Commercial loans \| Current \| Commercial construction
Financing Receivable, Past Due [Line Items]
Total	306,143	340,230
Commercial loans \| Current \| Business banking
Financing Receivable, Past Due [Line Items]
Total	1,309,315	1,297,651
Commercial loans \| Total Past Due Loans \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	34,799	3,228
Commercial loans \| Total Past Due Loans \| Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	24,744	13,584
Commercial loans \| Total Past Due Loans \| Commercial construction
Financing Receivable, Past Due [Line Items]
Total	869	1,036
Commercial loans \| Total Past Due Loans \| Business banking
Financing Receivable, Past Due [Line Items]
Total	7,031	5,607
Commercial loans \| 30-59 Days Past Due \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	9,151	0
Commercial loans \| 30-59 Days Past Due \| Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	15,765	415
Commercial loans \| 30-59 Days Past Due \| Commercial construction
Financing Receivable, Past Due [Line Items]
Total	0	0
Commercial loans \| 30-59 Days Past Due \| Business banking
Financing Receivable, Past Due [Line Items]
Total	2,358	2,336
Commercial loans \| 60-89 Days Past Due \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	0	0
Commercial loans \| 60-89 Days Past Due \| Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	0	1,996
Commercial loans \| 60-89 Days Past Due \| Commercial construction
Financing Receivable, Past Due [Line Items]
Total	0	1,036
Commercial loans \| 60-89 Days Past Due \| Business banking
Financing Receivable, Past Due [Line Items]
Total	527	283
Consumer loans \| Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	2,028,954	1,933,509
Nonaccrual	9,812	10,318	6,312
Consumer loans \| Other consumer
Financing Receivable, Past Due [Line Items]
Total	102,600	104,757
Nonaccrual	164	230	$ 330
Consumer loans \| Current \| Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	2,013,275	1,918,150
Consumer loans \| Current \| Other consumer
Financing Receivable, Past Due [Line Items]
Total	101,957	104,156
Consumer loans \| Total Past Due Loans \| Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	15,679	15,359
Consumer loans \| Total Past Due Loans \| Other consumer
Financing Receivable, Past Due [Line Items]
Total	643	601
Consumer loans \| 30-59 Days Past Due \| Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	2,763	2,464
Consumer loans \| 30-59 Days Past Due \| Other consumer
Financing Receivable, Past Due [Line Items]
Total	120	216
Consumer loans \| 60-89 Days Past Due \| Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	3,104	2,577
Consumer loans \| 60-89 Days Past Due \| Other consumer
Financing Receivable, Past Due [Line Items]
Total	$ 359	$ 155