Regulatory Capital - Summary of Regulatory Capital Requirement (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 519,613	$ 427,616
Total capital (to risk-weighted assets), Actual, Ratio	13.23%	13.39%
Total capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 314,113	$ 255,419
Total capital (to risk-weighted assets), For capital adequacy purposes, Ratio	8.00%	8.00%
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 412,273	$ 315,283
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	10.50%	9.875%
Tier 1 capital (to average assets), Actual, Amount	$ 501,272	$ 409,760
Tier 1 capital (to average assets), Actual, Ratio	12.77%	12.83%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 235,586	$ 191,565
Tier 1 capital (to average assets), For capital adequacy purpose, Ratio	6.00%	6.00%
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 333,747	$ 251,429
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	8.50%	7.875%
Common equity tier 1 capital, Actual Amount	$ 443,779	$ 371,297
Common equity tier 1 capital, Actual Ratio	11.30%	11.63%
Common equity tier 1 capital,For capital adequacy purposes, Amount	$ 176,689	$ 143,673
Common equity tier 1 capital, For capital adequacy purpose, Ratio	4.50%	4.50%
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 274,849	$ 203,537
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	7.00%	6.375%
Tier 1 capital (to average assets), Actual, Amount	$ 501,272	$ 409,760
Tier 1 capital (to average assets), Actual, Ratio	10.33%	10.12%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 194,081	$ 162,033
Tier 1 capital (to average assets), For capital adequacy purpose, Ratio	4.00%	4.00%
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 194,081	$ 162,033
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	4.00%	4.00%
Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 480,366	$ 396,755
Total capital (to risk-weighted assets), Actual, Ratio	12.23%	12.43%
Total capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 314,242	$ 255,419
Total capital (to risk-weighted assets), For capital adequacy purposes, Ratio	8.00%	8.00%
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 412,443	$ 315,283
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	10.50%	9.875%
Total capital (to risk-weighted assets), For well capitalized purpose, Amount	$ 392,802	$ 319,274
Total capital (to risk-weighted assets), For well capitalized purpose, Ratio	10.00%	10.00%
Tier 1 capital (to average assets), Actual, Amount	$ 462,025	$ 378,899
Tier 1 capital (to average assets), Actual, Ratio	11.76%	11.87%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 235,681	$ 191,565
Tier 1 capital (to average assets), For capital adequacy purpose, Ratio	6.00%	6.00%
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 333,881	$ 251,429
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	8.50%	7.875%
Tier 1 capital (to average assets), For well capitalized purpose, Amount	$ 314,241	$ 255,420
Tier 1 capital (to average assets), For well capitalized purposes, Ratio	8.00%	8.00%
Common equity tier 1 capital, Actual Amount	$ 462,025	$ 378,899
Common equity tier 1 capital, Actual Ratio	11.76%	11.87%
Common equity tier 1 capital,For capital adequacy purposes, Amount	$ 176,761	$ 143,674
Common equity tier 1 capital, For capital adequacy purpose, Ratio	4.50%	4.50%
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 274,961	$ 203,537
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	7.00%	6.375%
Common equity tier 1 capital, For well capitalized purpose, Amount	$ 255,321	$ 207,528
Common equity tier 1 capital, For well capitalized purposes, Ratio	6.50%	6.50%
Tier 1 capital (to average assets), Actual, Amount	$ 462,025	$ 378,899
Tier 1 capital (to average assets), Actual, Ratio	9.52%	9.34%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 194,081	$ 162,327
Tier 1 capital (to average assets), For capital adequacy purpose, Ratio	4.00%	4.00%
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Amount	$ 194,081	$ 162,327
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	4.00%	4.00%
Tier 1 capital (to average assets), For well capitalized purpose, Amount	$ 242,602	$ 202,908
Tier 1 capital (to average assets), For well capitalized purposes, Ratio	5.00%	5.00%