Earnings per Share - Calculations of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
	Mar. 25, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income attributable to Pathfinder Bancorp, Inc.		$ 12,407	$ 6,950
Convertible preferred stock dividends		$ 180	$ 291
Dividends per common share (Voting and Series A Non-Voting)	$ 0.09	$ 0.28	$ 0.24
Series A Nonvoting Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income attributable to Pathfinder Bancorp, Inc.		$ 1,542
Dividends per common share (Voting and Series A Non-Voting)		$ 206
Warrant dividends		$ 35
Undistributed earnings allocated to participating securities		$ 9,392
Basic weighted average common shares outstanding- Voting		745
Diluted weighted average common shares outstanding- Voting		745
Earnings per common share- basic		$ 2.07
Earnings per common share - diluted		2.07
Voting Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dividends per common share (Voting and Series A Non-Voting)		$ 1,258
Warrant dividends		$ 35	$ 30
Undistributed earnings allocated to participating securities		2,699	1,224
Net income available to common shareholders- Voting		$ 9,287	$ 5,405
Basic weighted average common shares outstanding- Voting		4,478	4,608
Diluted weighted average common shares outstanding- Voting		4,478	4,608
Earnings per common share- basic		$ 2.07	$ 1.17
Earnings per common share - diluted		$ 2.07	$ 1.17