Condensed Parent Company Only Financial Statements - Condensed Cash Flow Statements (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net Income	$ 2,457	$ 17,394	$ 16,926	$ 15,717	$ 15,118	$ 15,138	$ 14,833	$ 14,251	$ 52,494	$ 59,340	$ 58,421
Adjustments to reconcile net income to net cash provided by operating activities
Other, net									1,057	(2,093)	(9,631)
Investing activities
Other, net									2,576	119	(789)
Financing activities
Cash dividends									(27,627)	(26,603)	(25,411)
Repurchase of common shares									0	(1,166)	(3,505)
Redemption of trust preferred debentures									(21,161)	0	0
Shares issued for dividend reinvestment plans									2,872	3,201	0
Shares issued for employee stock ownership plan									2,296	1,938	1,595
Net proceeds from stock option exercises									(641)	(806)	1,382
Common stock issued									0	0	50
Net Increase in Cash and Cash Equivalents									20,349	5,697	2,187
Cash and cash equivalents at beginning of year				63,954				58,257	63,954	58,257	56,070
Total Cash & Cash Equivalents at End of Year	84,303				63,954				84,303	63,954	58,257
Tompkins (the Parent Company)
Operating activities
Net Income									52,494	59,340	58,421
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed earnings of subsidiaries									(24,494)	(16,770)	(34,816)
Other, net									(1,569)	1,826	1,511
Net Cash Provided by Operating Activities									26,431	44,396	25,116
Investing activities
Other, net									1,052	24	81
Net Cash Provided by Investing Activities									1,052	24	81
Financing activities
Borrowings, net									(28,161)	2,490	0
Cash dividends									(27,627)	(26,603)	(25,411)
Repurchase of common shares									0	(1,166)	(3,505)
Redemption of trust preferred debentures									(1,294)	(835)	(195)
Shares issued for dividend reinvestment plans									2,872	3,201	0
Shares issued for employee stock ownership plan									2,296	1,938	1,595
Net proceeds from stock option exercises									(641)	(806)	1,382
Common stock issued									0	0	50
Net Cash Used in Financing Activities									(52,555)	(21,781)	(26,084)
Net Increase in Cash and Cash Equivalents									(25,072)	22,639	(887)
Cash and cash equivalents at beginning of year				$ 28,398				$ 5,759	28,398	5,759	6,646
Total Cash & Cash Equivalents at End of Year	$ 3,326				$ 28,398				$ 3,326	$ 28,398	$ 5,759