Regulatory Capital Requirements (Details) $ in Thousands		Sep. 30, 2020 USD ($) Classification	Dec. 31, 2019 USD ($)
Trustco Bank [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations Information [Abstract]
Number of classifications for prompt corrective action regulations provide | Classification		5
Tier One Risk Based Capital [Abstract]
Tier 1 leverage capital		$ 533,874	$ 516,775
Common equity Tier 1 capital		533,874	516,775
Tier 1 risk-based capital		533,874	516,775
Total risk-based capital		$ 570,127	$ 551,975
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		0.09329	0.09940
Common equity Tier 1 capital, ratio		0.18491	0.18412
Tier 1 risk-based capital, ratio		0.18491	0.18412
Total risk-based capital, ratio		0.19747	0.19666
Leverage Ratios [Abstract]
Tier 1 leverage ratio, well capitalized	[1]	0.05000	0.05000
Tier 1 leverage ratio, minimum for capital adequacy plus capital conservation	[1],[2]	0.04000	0.04000
Common equity Tier 1 capital, well capitalized	[1]	0.06500	0.06500
Common equity Tier 1 capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.07000	0.07000
Tier 1 risk-based capital, well capitalized	[1]	0.08000	0.08000
Tier 1 risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.08500	0.08500
Total risk-based capital, well capitalized	[1]	0.10000	0.10000
Total risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.10500	0.10500
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		0.0250	0.0250
Tier 1 risk based capital ratio, capital conservation buffer		0.0250	0.0250
Total risk based capital ratio, capital conservation buffer		0.0250	0.0250
TrustCo Bank Corp NY [Member]
Tier One Risk Based Capital [Abstract]
Tier 1 leverage capital		$ 548,437	$ 533,243
Common equity Tier 1 capital		548,437	533,243
Tier 1 risk-based capital		548,437	533,243
Total risk-based capital		$ 584,692	$ 568,463
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		0.09582	0.10254
Common equity Tier 1 capital, ratio		0.18994	0.18988
Tier 1 risk-based capital, ratio		0.18994	0.18988
Total risk-based capital, ratio		0.20250	0.20242
Leverage Ratios [Abstract]
Tier 1 leverage ratio, minimum for capital adequacy plus capital conservation	[1],[2]	0.04000	0.04000
Common equity Tier 1 capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.07000	0.07000
Tier 1 risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.08500	0.08500
Total risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	0.10500	0.10500
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		0.0250	0.0250
Tier 1 risk based capital ratio, capital conservation buffer		0.0250	0.0250
Total risk based capital ratio, capital conservation buffer		0.0250	0.0250

[1] Federal regulatory minimum requirements to be considered to be Well Capitalized and Adequately Capitalized

[2] The September 30, 2020 and December 31, 2019 common equity tier 1, tier 1 risk-based, and total risk-based capital ratios include a capital conservation buffer of 2.50 percent