Regulatory Matters - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Total Capital (to Risk-Weighted Assets):
Total Capital (to Risk-Weighted Assets) actual, amount	$ 655,010	$ 604,213
Total Capital (to Risk-Weighted Assets) actual, ratio	13.78%	13.70%
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, amount	$ 380,276	$ 352,764
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, ratio	8.00%	8.00%
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 475,344	$ 440,955
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	10.00%	10.00%
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital (to Risk-Weighted Assets) actual, Amount	$ 524,137	$ 479,550
Tier 1 Capital (to Risk-Weighted Assets) Actual, ratio	11.03%	10.88%
Tier 1 Capital (to Risk - Weighed Assets) For Capital Adequacy, amount	$ 285,207	$ 264,573
Tier 1 Capital (to Risk - Weighted Assets) For Capital Adequacy, ratio	6.00%	6.00%
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 380,276	$ 352,764
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	8.00%	8.00%
Tier 1 Common Capital (to Risk-Weighted Assets)
Tier One Common Risk Based Capital	$ 524,137	$ 479,550
Tier One Common Risk Based Capital To Risk Weighted Assets	11.03%	10.88%
Tier One Common Risk Based Capital Required For Capital Adequacy	$ 213,905	$ 198,430
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	$ 308,974	$ 286,621
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	$ 524,137	$ 479,550
Tier 1 Capital (to Average Assets) actual, ratio	10.02%	10.13%
Tier 1 Capital (to Average Assets) For Capital Adequacy, amount	$ 209,330	$ 189,374
Tier 1 Capital (to Average Assets) For Capital Adequacy, ratio	4.00%	4.00%
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 261,663	$ 236,718
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	5.00%	5.00%
Bank [Member]
Total Capital (to Risk-Weighted Assets):
Total Capital (to Risk-Weighted Assets) actual, amount	$ 552,142	$ 506,728
Total Capital (to Risk-Weighted Assets) actual, ratio	11.66%	11.54%
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, amount	$ 378,724	$ 351,220
Total Capital (to Risk-Weighted Assets) For Capital Adequacy, ratio	8.00%	8.00%
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 473,405	$ 439,026
Total Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	10.00%	10.00%
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital (to Risk-Weighted Assets) actual, Amount	$ 516,087	$ 476,639
Tier 1 Capital (to Risk-Weighted Assets) Actual, ratio	10.90%	10.86%
Tier 1 Capital (to Risk - Weighed Assets) For Capital Adequacy, amount	$ 284,043	$ 263,415
Tier 1 Capital (to Risk - Weighted Assets) For Capital Adequacy, ratio	6.00%	6.00%
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 378,724	$ 351,220
Tier 1 Capital (to Risk-Weighted Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	8.00%	8.00%
Tier 1 Common Capital (to Risk-Weighted Assets)
Tier One Common Risk Based Capital	$ 516,087	$ 476,639
Tier One Common Risk Based Capital To Risk Weighted Assets	10.90%	10.86%
Tier One Common Risk Based Capital Required For Capital Adequacy	$ 213,032	$ 197,561
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	$ 307,713	$ 285,367
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	$ 516,087	$ 476,639
Tier 1 Capital (to Average Assets) actual, ratio	9.90%	10.12%
Tier 1 Capital (to Average Assets) For Capital Adequacy, amount	$ 208,589	$ 188,487
Tier 1 Capital (to Average Assets) For Capital Adequacy, ratio	4.00%	4.00%
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, amount	$ 260,737	$ 235,609
Tier 1 Capital (to Average Assets) To Be Well Capitalized Under Prompt Corrective Action Provisions, ratio	5.00%	5.00%