Regulatory Capital Requirements (Details) $ in Thousands		Sep. 30, 2019 USD ($) Classification		Dec. 31, 2018 USD ($)
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		$ 509,531		$ 484,581
Common equity Tier 1 capital		509,531		484,581
Tier 1 risk-based capital		509,531		484,581
Total risk-based capital		$ 544,641		$ 517,948
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		9.751%		9.767%
Common equity Tier 1 capital, ratio		18.202%		18.233%
Tier 1 risk-based capital, ratio		18.202%		18.233%
Total risk-based capital, ratio		19.456%		19.489%
Leverage Ratios [Abstract]
Tier 1 leverage ratio, well capitalized	[1]	5.00%		5.00%
Tier 1 leverage ratio, adequately capitalized	[1]	4.00%	[2]	4.00%	[3]
Common equity Tier 1 capital, well capitalized	[1]	6.50%		6.50%
Common equity Tier 1 capital, adequately capitalized	[1]	7.00%	[2]	6.38%	[3]
Tier 1 risk-based capital, well capitalized	[1]	8.00%		8.00%
Tier 1 risk-based capital, adequately capitalized	[1]	8.50%	[2]	7.88%	[3]
Total risk-based capital, well capitalized	[1]	10.00%		10.00%
Total risk-based capital, adequately capitalized	[1]	10.50%	[2]	9.88%	[3]
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		2.50%		1.88%
Tier 1 risk based capital ratio, capital conservation buffer		2.50%		1.88%
Total risk based capital ratio, capital conservation buffer		2.50%		1.88%
TrustCo Bank Corp NY [Member]
Tier One Risk Based Capital [Abstract]
Tier 1 leverage capital		$ 525,680		$ 499,626
Common equity Tier 1 capital		525,680		499,626
Tier 1 risk-based capital		525,680		499,626
Total risk-based capital		$ 560,811		$ 533,009
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		10.057%		10.129%
Common equity Tier 1 capital, ratio		18.767%		18.79%
Tier 1 risk-based capital, ratio		18.767%		18.79%
Total risk-based capital, ratio		20.021%		20.046%
Leverage Ratios [Abstract]
Tier 1 leverage ratio, adequately capitalized	[1],[2]	4.00%		4.00%
Common equity Tier 1 capital, adequately capitalized	[1],[2]	7.00%		6.38%
Tier 1 risk-based capital, adequately capitalized	[1],[2]	8.50%		7.88%
Total risk-based capital, adequately capitalized	[1],[2]	10.50%		9.88%
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		2.50%		1.88%
Tier 1 risk based capital ratio, capital conservation buffer		2.50%		1.88%
Total risk based capital ratio, capital conservation buffer		2.50%		1.88%

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

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

[3] The December 31, 2018 common equity tier 1, tier 1 risk-based, and total risk-based capital ratios include a transition capital conservation buffer of 1.88 percent