Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Parent
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 825,099	$ 793,433
Tier 1 Capital (to Risk Weighted Assets)	756,668	727,879
Common Equity Tier 1 Capital (to Risk Weighted Assets)	700,660	671,975
Tier 1 Capital (to Average Assets)	$ 756,668	$ 727,879
Total Capital Ratio (to Risk Weighted Assets)	15.13%	15.22%
Tier 1 Capital Ratio (to Risk Weighted Assets)	13.88%	13.96%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	12.85%	12.89%
Tier 1 Capital Ratio (to Average Assets)	10.00%	9.93%
Parent \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 572,425	$ 547,352
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	463,392	443,094
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	381,617	364,901
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 302,730	$ 293,138
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)	$ 812,092	$ 780,320
Tier 1 Capital (to Risk Weighted Assets)	743,705	714,811
Common Equity Tier 1 Capital (to Risk Weighted Assets)	743,705	714,811
Tier 1 Capital (to Average Assets)	$ 743,705	$ 714,811
Total Capital Ratio (to Risk Weighted Assets)	14.90%	14.97%
Tier 1 Capital Ratio (to Risk Weighted Assets)	13.65%	13.72%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	13.65%	13.72%
Tier 1 Capital Ratio (to Average Assets)	9.84%	9.76%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 544,980	$ 521,101
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	$ 435,984	$ 416,881
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	$ 354,237	$ 338,716
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	$ 377,981	$ 366,186
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	$ 572,229	$ 547,156
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	463,233	442,936
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	381,486	364,771
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 302,385	$ 292,949
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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