Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Parent
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	$ 793,433	$ 753,200
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	727,879	719,809
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	671,975	664,296
Tier 1 Capital (to Average Assets), Actual, Amount	$ 727,879	$ 719,809
Total Capital (to Risk Weighted Assets), Actual, Ratio	15.22%	15.07%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.96%	14.40%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	12.89%	13.29%
Tier 1 Capital (to Average Assets), Actual, Ratio	9.93%	11.55%
Parent \| Required for Capital Adequacy Purposes
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	$ 547,352	$ 524,944
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	443,094	424,955
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	364,901	349,963
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 293,138	$ 249,343
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%	8.50%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%	7.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	4.00%
Tri Counties Bank
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	$ 780,320	$ 748,660
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	714,811	715,269
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	714,811	715,269
Tier 1 Capital (to Average Assets), Actual, Amount	$ 714,811	$ 715,269
Total Capital (to Risk Weighted Assets), Actual, Ratio	14.97%	14.98%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.72%	14.31%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.72%	14.31%
Tier 1 Capital (to Average Assets), Actual, Ratio	9.76%	11.47%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 521,101	$ 499,770
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	416,881	399,816
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	338,716	324,851
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 366,186	$ 311,672
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%
Tri Counties Bank \| Required for Capital Adequacy Purposes
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	$ 547,156	$ 524,759
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	442,936	424,805
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	364,771	349,839
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 292,949	$ 249,337
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%	8.50%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%	7.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	4.00%

Common Equity Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets

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The amount of total capital as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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