Segment and Related Information - Narrative (Details)	9 Months Ended
	Sep. 30, 2021 subsidiary_Bank banking_Office segment office
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
Nature of operations, number of subsidiary banks | subsidiary_Bank	4
Tompkins, Cayuga, Cortland and Schuyler Counties, New York
Segment Reporting Information [Line Items]
Nature of operations, number of banking offices	13
Wyoming, Livingston, Genessee, Orleans and Monroe, New York
Segment Reporting Information [Line Items]
Nature of operations, number of banking offices	16
Putnam Country, Dutchess Country and Westchester, New York
Segment Reporting Information [Line Items]
Nature of operations, number of banking offices	14
Berks, Montgomery, Philadelphia, Deleware and Schuylkill, Pennsylvania
Segment Reporting Information [Line Items]
Nature of operations, number of banking offices	20
Western New York
Segment Reporting Information [Line Items]
Number of offices | office	5
Tompkins Insurance Agencies Inc
Segment Reporting Information [Line Items]
Noncontrolling interest, ownership percentage by parent	100.00%