Summary of Significant Accounting Policies - Summary of Bank's Actual Capital Amounts and Ratios, and the Regulatory Minimum Ratios (Detail) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounting Policies [Abstract]
Regulatory, Minimum, Leverage ratio	[1]	0.04
Regulatory, Minimum, Common equity tier 1 capital ratio	[2]	7.00%
Regulatory, Minimum, Tier 1 capital ratio	[3]	8.50%
Regulatory, Minimum, Total capital ratio	[3]	0.105
Regulatory, Well-Capitalized, Leverage ratio	[1]	0.05
Regulatory, Well-Capitalized, Common equity tier 1 capital ratio	[2]	6.50%
Regulatory, Well-Capitalized, Tier 1 capital ratio	[3]	0.08
Regulatory, Well-Capitalized, Total capital ratio	[3]	0.10
Common equity Tier 1 capital		$ 283,342	$ 242,049
Tier 1 capital		352,130	310,837
Total capital		379,754	334,913
Average assets		2,190,234	1,917,904
Risk-weighted assets		$ 2,162,430	$ 1,888,530
Leverage ratio	[1]	0.161	0.162
Common equity Tier 1 capital ratio	[2]	0.131	0.128
Tier 1 capital ratio	[3]	0.163	0.165
Total capital ratio	[3]	0.176	0.177

[1] Calculated by dividing Tier 1 capital by average assets.

[2] Calculated by subtracting preferred stock or non-controlling interest from Tier 1 capital and dividing by risk-weighted assets.

[3] Calculated by dividing Tier 1 or total capital by risk-weighted assets. With the adoption of CECL on January 1, 2023 the Bank elected to phase in the regulatory capital effects of the transition amount, which reduced the capital impact by $6.2 million and increased the Tier 1 capital ratio by 27 basis points.