Earnings per Common Share - Calculations of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to Pathfinder Bancorp, Inc.	$ 607	$ 945	$ 1,121	$ 1,949
Convertible preferred stock dividends	69		69
Warrant dividend	8		8
Undistributed earnings allocated to participating securities	38		41
Net Income available to common shareholders	$ 492	$ 945	$ 1,003	$ 1,949
Basic weighted average common shares outstanding (in shares)	4,443	4,157	4,344	4,138
Effect of assumed exercise of stock options and unvested restricted stock units (in shares)		99		108
Diluted weighted average common shares outstanding (in shares)	4,443	4,256	4,344	4,246
Earnings per common share - basic	$ 0.11	$ 0.23	$ 0.23	$ 0.47
Earnings per common share - diluted	$ 0.11	$ 0.22	$ 0.23	$ 0.46