Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Consolidated
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets)	$ 1,177,733	$ 1,115,257
Tier 1 Capital (to Risk Weighted Assets)	1,033,710	974,325
Common Equity Tier 1 Capital (to Risk Weighted Assets)	976,657	917,565
Tier 1 Capital (to Average Assets)	$ 1,033,710	$ 974,325
Total Capital Ratio (to Risk Weighted Assets)	0.1451	0.1419
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1273	0.1240
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1203	0.1167
Tier 1 Capital Ratio (to Average Assets)	0.1060	0.1014
Consolidated \| Basel III Fully Phased In
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement	$ 852,532	$ 825,234
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	690,145	668,047
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	568,355	550,156
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 389,994	$ 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)	$ 1,172,064	$ 1,107,941
Tier 1 Capital (to Risk Weighted Assets)	1,070,347	1,009,577
Common Equity Tier 1 Capital (to Risk Weighted Assets)	1,070,347	1,009,577
Tier 1 Capital (to Average Assets)	$ 1,070,347	$ 1,009,577
Total Capital Ratio (to Risk Weighted Assets)	0.1444	0.1410
Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1319	0.1285
Common Equity Tier 1 Capital Ratio (to Risk Weighted Assets)	0.1319	0.1285
Tier 1 Capital Ratio (to Average Assets)	0.1098	0.1051
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 811,738	$ 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	$ 649,391	$ 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	$ 527,630	$ 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	$ 487,441	$ 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	$ 852,325	$ 825,039
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	689,978	667,888
Common Equity Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement	568,217	550,026
Tier 1 Capital (to Average Assets), Minimum Capital Requirement	$ 389,953	$ 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

Common Equity Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480696/942-505-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
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-Section 50
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