Regulatory Matters - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Detail) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Total Capital (to Risk-Weighted Assets):
Total Capital (to Risk-Weighted Assets) actual, amount	$ 801,368	$ 655,010
Total Capital (to Risk-Weighted Assets) actual, ratio	0.1531	0.1378
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, amount	$ 418,811	$ 380,276
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, ratio	0.0800	0.0800
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 523,513	$ 475,344
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.1000	0.1000
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital (to Risk-Weighted Assets) actual, Amount	$ 563,491	$ 524,137
Tier 1 Capital (to Risk-Weighted Assets) Actual, ratio	0.1076	0.1103
Tier 1 Capital (to Risk - Weighed Assets) For Capital Adequacy, amount	$ 314,108	$ 285,207
Tier 1 Capital (to Risk - Weighted Assets) For Capital Adequacy, ratio	0.0600	0.0600
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 418,811	$ 380,276
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.0800	0.0800
Tier 1 Common Capital (to Risk-Weighted Assets)
Tier One Common Risk Based Capital	$ 563,491	$ 524,137
Tier One Common Risk Based Capital To Risk Weighted Assets	10.76%	11.03%
Tier One Common Risk Based Capital Required For Capital Adequacy	$ 235,581	$ 213,905
Tier One Common Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets	4.50%	4.50%
Tier One Common Risk Based Capital Required To Be Well Capitalized	$ 340,284	$ 308,974
Tier One Common Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets	6.50%	6.50%
Tier 1 Capital (to Average Assets):
Tier 1 Capital (to Average Assets) actual, amount	$ 563,491	$ 524,137
Tier 1 Capital (to Average Assets) actual, ratio	0.0908	0.1002
Tier 1 Capital (to Average Assets) For Capital Adequacy, amount	$ 248,224	$ 209,330
Tier 1 Capital (to Average Assets) For Capital Adequacy, ratio	0.0400	0.0400
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 310,280	$ 261,663
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.0500	0.0500
Bank [Member]
Total Capital (to Risk-Weighted Assets):
Total Capital (to Risk-Weighted Assets) actual, amount	$ 632,183	$ 552,142
Total Capital (to Risk-Weighted Assets) actual, ratio	0.1212	0.1166
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, amount	$ 417,416	$ 378,724
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, ratio	0.0800	0.0800
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 521,769	$ 473,405
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.1000	0.1000
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital (to Risk-Weighted Assets) actual, Amount	$ 569,821	$ 516,087
Tier 1 Capital (to Risk-Weighted Assets) Actual, ratio	0.1092	0.1090
Tier 1 Capital (to Risk - Weighed Assets) For Capital Adequacy, amount	$ 313,062	$ 284,043
Tier 1 Capital (to Risk - Weighted Assets) For Capital Adequacy, ratio	0.0600	0.0600
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 417,416	$ 378,724
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.0800	0.0800
Tier 1 Common Capital (to Risk-Weighted Assets)
Tier One Common Risk Based Capital	$ 569,821	$ 516,087
Tier One Common Risk Based Capital To Risk Weighted Assets	10.92%	10.90%
Tier One Common Risk Based Capital Required For Capital Adequacy	$ 234,796	$ 213,032
Tier One Common Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets	4.50%	4.50%
Tier One Common Risk Based Capital Required To Be Well Capitalized	$ 339,150	$ 307,713
Tier One Common Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets	6.50%	6.50%
Tier 1 Capital (to Average Assets):
Tier 1 Capital (to Average Assets) actual, amount	$ 569,821	$ 516,087
Tier 1 Capital (to Average Assets) actual, ratio	0.0921	0.0990
Tier 1 Capital (to Average Assets) For Capital Adequacy, amount	$ 247,494	$ 208,589
Tier 1 Capital (to Average Assets) For Capital Adequacy, ratio	0.0400	0.0400
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 309,368	$ 260,737
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	0.0500	0.0500