Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) $ in Thousands	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Consolidated
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 869,196	$ 793,433
Tier 1 Capital (to Risk Weighted Assets)	798,433	727,879
Common Equity Tier 1 Capital (to Risk Weighted Assets)	742,209	671,975
Tier 1 Capital (to Average Assets)	$ 798,433	$ 727,879
Total Capital Ratio (to Risk Weighted Assets)	0.1541	0.1522
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1415	0.1396
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1315	0.1289
Tier 1 Capital Ratio (to Average Assets)	0.0985	0.0993
Consolidated \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 592,435	$ 547,352
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	479,590	443,094
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	394,957	364,901
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 324,391	$ 293,138
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	0.1050	0.1050
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	0.0850	0.0850
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	0.0400	0.0400
Tri Counties Bank
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 860,080	$ 780,320
Tier 1 Capital (to Risk Weighted Assets)	789,416	714,811
Common Equity Tier 1 Capital (to Risk Weighted Assets)	789,416	714,811
Tier 1 Capital (to Average Assets)	$ 789,416	$ 714,811
Total Capital Ratio (to Risk Weighted Assets)	0.1526	0.1497
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1401	0.1372
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1401	0.1372
Tier 1 Capital Ratio (to Average Assets)	0.0974	0.0976
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 563,595	$ 521,101
Capital Required to be Well Capitalized to Risk Weighted Assets	0.1000	0.1000
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 450,876	$ 416,881
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	0.0800	0.0800
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 366,337	$ 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	$ 405,317	$ 366,186
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	0.0500	0.0500
Tri Counties Bank \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 591,775	$ 547,156
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	479,056	442,936
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	394,517	364,771
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 324,254	$ 292,949
Total Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	0.1050	0.1050
Tier 1 Capital Ratio (to Risk Weighted Assets), Minimum Capital Requirement	0.0850	0.0850
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	0.0400	0.0400

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