Regulatory Capital Requirements (Details) $ in Thousands		Mar. 31, 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		$ 522,527	$ 516,775
Common equity Tier 1 capital		522,527	516,775
Tier 1 risk-based capital		522,527	516,775
Total risk-based capital		$ 558,027	$ 551,975
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		10.058%	9.94%
Common equity Tier 1 capital, ratio		18.47%	18.412%
Tier 1 risk-based capital, ratio		18.47%	18.412%
Total risk-based capital, ratio		19.724%	19.666%
Leverage Ratios [Abstract]
Tier 1 leverage ratio, well capitalized	[1]	5.00%	5.00%
Tier 1 leverage ratio, minimum for capital adequacy plus capital conservation	[1],[2]	4.00%	4.00%
Common equity Tier 1 capital, well capitalized	[1]	6.50%	6.50%
Common equity Tier 1 capital, minimum for capital adequacy plus capital conservation	[1],[2]	7.00%	7.00%
Tier 1 risk-based capital, well capitalized	[1]	8.00%	8.00%
Tier 1 risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	8.50%	8.50%
Total risk-based capital, well capitalized	[1]	10.00%	10.00%
Total risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	10.50%	10.50%
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		2.50%	2.50%
Tier 1 risk based capital ratio, capital conservation buffer		2.50%	2.50%
Total risk based capital ratio, capital conservation buffer		2.50%	2.50%
TrustCo Bank Corp NY [Member]
Tier One Risk Based Capital [Abstract]
Tier 1 leverage capital		$ 536,239	$ 533,243
Common equity Tier 1 capital		536,239	533,243
Tier 1 risk-based capital		536,239	533,243
Total risk-based capital		$ 571,760	$ 568,463
Risk Based Ratios [Abstract]
Tier 1 leverage ratio, ratio		10.316%	10.254%
Common equity Tier 1 capital, ratio		18.943%	18.988%
Tier 1 risk-based capital, ratio		18.943%	18.988%
Total risk-based capital, ratio		20.198%	20.242%
Leverage Ratios [Abstract]
Tier 1 leverage ratio, minimum for capital adequacy plus capital conservation	[1],[2]	4.00%	4.00%
Common equity Tier 1 capital, minimum for capital adequacy plus capital conservation	[1],[2]	7.00%	7.00%
Tier 1 risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	8.50%	8.50%
Total risk-based capital, minimum for capital adequacy plus capital conservation	[1],[2]	10.50%	10.50%
Capital Conservation Buffer [Abstract]
Common equity Tier 1 capital conservation buffer		2.50%	2.50%
Tier 1 risk based capital ratio, capital conservation buffer		2.50%	2.50%
Total risk based capital ratio, capital conservation buffer		2.50%	2.50%

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

[2] The March 31, 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