Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Parent
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 774,095	$ 753,200
Tier 1 Capital (to Risk Weighted Assets)	710,195	719,809
Common Equity Tier 1 Capital (to Risk Weighted Assets)	654,396	664,296
Tier 1 Capital (to Average Assets)	$ 710,195	$ 719,809
Total Capital Ratio (to Risk Weighted Assets)	15.23%	15.07%
Tier 1 Capital Ratio (to Risk Weighted Assets)	13.97%	14.40%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	12.87%	13.29%
Tier 1 Capital Ratio (to Average Assets)	9.95%	11.55%
Parent \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 533,776	$ 524,944
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	432,104	424,955
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	355,850	349,963
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 285,482	$ 249,343
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	10.50%	10.50%
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	8.50%	8.50%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	7.00%	7.00%
Tier 1 Capital Ratio (to Average Assets), Minimum Capital Requirement	4.00%	4.00%
Tri Countries Bank
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 769,528	$ 748,660
Tier 1 Capital (to Risk Weighted Assets)	705,673	715,269
Common Equity Tier 1 Capital (to Risk Weighted Assets)	705,673	715,269
Tier 1 Capital (to Average Assets)	$ 705,673	$ 715,269
Total Capital Ratio (to Risk Weighted Assets)	15.14%	14.98%
Tier 1 Capital Ratio (to Risk Weighted Assets)	13.89%	14.31%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	13.89%	14.31%
Tier 1 Capital Ratio (to Average Assets)	9.89%	11.47%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 508,166	$ 499,770
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 406,533	$ 399,816
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 330,308	$ 324,851
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 356,845	$ 311,672
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Tri Countries Bank \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 533,575	$ 524,759
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	431,941	424,805
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	355,716	349,839
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 285,476	$ 249,337
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	10.50%	10.50%
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	8.50%	8.50%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	7.00%	7.00%
Tier 1 Capital Ratio (to Average Assets), Minimum Capital Requirement	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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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Amount of Common Equity Tier One Risk-based Capital, as defined by regulatory framework.

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