Accumulated Other Comprehensive (Loss) Income - Summary of Amounts Reclassified Out of Each Component of AOCI (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits		$ (4,959)	$ (4,154)	$ (13,687)	$ (12,243)
Provision for income taxes		1,173	(573)	160	(1,772)
Net (loss) income attributable to Pathfinder Bancorp Inc.		(4,644)	2,176	(524)	6,757
Reclassification out of Accumulated Other Comprehensive Income [Member] | Retirement Plans [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	[1],[2]	(38)	(56)	(113)	(167)
Provision for income taxes	[1]	10	15	30	44
Net (loss) income attributable to Pathfinder Bancorp Inc.	[1]	(28)	(41)	(83)	(123)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net gains on sales and redemptions of investment securities	[1]	0	1	(139)	(1,932)
Provision for income taxes	[1]	0	0	36	506
Net (loss) income attributable to Pathfinder Bancorp Inc.	[1]	$ 0	$ 1	$ (103)	$ (1,426)

[1] Amounts in parentheses indicates debits in net income.

[2] These items are included in net periodic pension cost.