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Goodwill and Other Acquisition-Related Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Sep. 01, 2026
Indefinite-lived Intangible Assets [Line Items]
Goodwill recorded on acquisition			$ 7,498
Business combination, intangible assets acquired	$ 34,100		34,100
Amortization of other acquisition-related intangible assets	4,686	$ 5,196	14,565	$ 16,394
Customer Relationships
Indefinite-lived Intangible Assets [Line Items]
Business combination, intangible assets acquired	$ 26,600		26,600
Specialty finance
Indefinite-lived Intangible Assets [Line Items]
Goodwill recorded on acquisition			0
Goodwill transfer			$ 11,300
Specialty finance \| Customer list intangibles
Indefinite-lived Intangible Assets [Line Items]
Amortization period in years, other intangible assets	18 years		18 years
Community Banking
Indefinite-lived Intangible Assets [Line Items]
Goodwill recorded on acquisition			$ 0
Community Banking \| Core deposit intangibles
Indefinite-lived Intangible Assets [Line Items]
Amortization period in years, other intangible assets	10 years		10 years
Wealth management
Indefinite-lived Intangible Assets [Line Items]
Goodwill recorded on acquisition			$ 7,498
Wealth management \| Customer list and other intangibles
Indefinite-lived Intangible Assets [Line Items]
Amortization period in years, other intangible assets	15 years		15 years
Northern Trust Corporation Guardianship Services Business
Indefinite-lived Intangible Assets [Line Items]
Assets					$ 1,200,000