Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Capitalization [Line Items]
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Parent
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 735,884	$ 682,419
Tier 1 Capital (to Risk Weighted Assets)	701,703	647,262
Common Equity Tier 1 Capital (to Risk Weighted Assets)	646,240	591,933
Tier 1 Capital (to Average Assets)	$ 701,703	$ 647,262
Total Capital Ratio (to Risk Weighted Assets)	15.23%	14.40%
Tier 1 Capital Ratio (to Risk Weighted Assets)	14.52%	13.66%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	13.37%	12.49%
Tier 1 Capital Ratio (to Average Assets)	11.31%	10.68%
Parent \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 507,335	$ 497,486
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	410,700	402,727
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	338,224	331,658
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 248,073	$ 242,452
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%
Parent \| Basel Three Phased In Schedule
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement		$ 467,874
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement		373,115
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement		302,045
Tier 1 Capital (to Average Assets), Minimum Capital Requirement		$ 242,452
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		9.875%
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		7.875%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		6.375%
Tier 1 Capital Ratio (to Average Assets), Minimum Capital Requirement		4.00%
Tri Countries Bank
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 731,359	$ 680,624
Tier 1 Capital (to Risk Weighted Assets)	697,178	645,467
Common Equity Tier 1 Capital (to Risk Weighted Assets)	697,178	645,467
Tier 1 Capital (to Average Assets)	$ 697,178	$ 645,467
Total Capital Ratio (to Risk Weighted Assets)	15.14%	14.37%
Tier 1 Capital Ratio (to Risk Weighted Assets)	14.43%	13.63%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	14.43%	13.63%
Tier 1 Capital Ratio (to Average Assets)	11.24%	10.65%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 483,002	$ 473,624
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	386,401	378,899
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	313,951	307,856
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	310,085	303,059
Tri Countries Bank \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	507,152	497,305
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	410,551	402,581
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	338,101	331,537
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 248,068	$ 242,447
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 \| Basel Three Phased In Schedule
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement		$ 467,704
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement		372,979
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement		301,935
Tier 1 Capital (to Average Assets), Minimum Capital Requirement		$ 242,447
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		9.875%
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		7.875%
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement		6.375%
Tier 1 Capital Ratio (to Average Assets), Minimum Capital Requirement		4.00%

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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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