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, 2024 USD ($)	Dec. 31, 2023 USD ($)
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		$ 314,153	$ 293,774
Tier 1 capital		382,940	362,561
Total capital		413,973	390,153
Average assets		2,444,674	2,232,816
Risk-weighted assets		$ 2,422,854	$ 2,155,641
Leverage ratio	[1]	0.157	0.162
Common equity Tier 1 capital ratio	[2]	0.13	0.136
Tier 1 capital ratio	[3]	0.158	0.168
Total capital ratio	[3]	0.171	0.181

[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.