Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) $ in Thousands	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Consolidated
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 1,134,613	$ 1,115,257
Tier 1 Capital (to Risk Weighted Assets)	994,155	974,325
Common Equity Tier 1 Capital (to Risk Weighted Assets)	937,300	917,565
Tier 1 Capital (to Average Assets)	$ 994,155	$ 974,325
Total Capital Ratio (to Risk Weighted Assets)	0.1450	0.1419
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1270	0.1240
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1198	0.1167
Tier 1 Capital Ratio (to Average Assets)	0.1020	0.1014
Consolidated \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 821,668	$ 825,234
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	665,160	668,047
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	547,779	550,156
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 393,017	$ 384,337
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)	$ 1,127,852	$ 1,107,941
Tier 1 Capital (to Risk Weighted Assets)	1,029,875	1,009,577
Common Equity Tier 1 Capital (to Risk Weighted Assets)	1,029,875	1,009,577
Tier 1 Capital (to Average Assets)	$ 1,029,875	$ 1,009,577
Total Capital Ratio (to Risk Weighted Assets)	0.1442	0.1410
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1316	0.1285
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1316	0.1285
Tier 1 Capital Ratio (to Average Assets)	0.1057	0.1051
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 782,352	$ 785,751
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	$ 625,882	$ 628,601
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	$ 508,529	$ 510,738
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	$ 491,091	$ 480,183
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	$ 821,470	$ 825,039
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	665,000	667,888
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	547,647	550,026
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 392,873	$ 384,146
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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