Segment and Related Information - Narrative (Details) - 12 months ended Dec. 31, 2018	segment	banking_office	subsidiary_bank	subsidiary_trust	office
Segment Reporting Information [Line Items]
Number of reportable business segments | segment	3
Number of subsidiary banks		4	3	4
Ithaca, NY
Segment Reporting Information [Line Items]
Number of banking offices		14
Genesee Valley Region
Segment Reporting Information [Line Items]
Number of banking offices		18
Counties North of New York City
Segment Reporting Information [Line Items]
Number of banking offices		14
Southeastern Pennsylvania
Segment Reporting Information [Line Items]
Number of banking offices		20
Western New York
Segment Reporting Information [Line Items]
Nature of operations, number of offices | office					5