Regulatory Capital - Summary of Regulatory Capital Requirement (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Regulatory Assets And Liabilities [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 320,710	$ 316,576
Total capital (to risk-weighted assets), Actual, Ratio	13.87%	13.87%
Total capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 185,042	$ 182,596
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	$ 199,614	$ 196,976
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	8.63%	8.63%
Tier 1 capital (to average assets), Actual, Amount	$ 305,656	$ 301,739
Tier 1 capital (to average assets), Actual, Ratio	13.21%	13.22%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 138,781	$ 136,947
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	$ 153,353	$ 151,326
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	6.63%	6.63%
Common equity tier 1 capital, Actual Amount	$ 267,193	$ 263,313
Common equity tier 1 capital, Actual Ratio	11.55%	11.50%
Common equity tier 1 capital,For capital adequacy purposes, Amount	$ 104,086	$ 103,036
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	$ 118,658	$ 117,460
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	5.13%	5.13%
Tier 1 capital (to average assets), Actual, Amount	$ 305,656	$ 301,739
Tier 1 capital (to average assets), Actual, Ratio	10.09%	10.44%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 121,213	$ 115,609
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	$ 121,213	$ 115,609
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	4.00%	4.00%
Bank [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 320,418	$ 319,013
Total capital (to risk-weighted assets), Actual, Ratio	13.87%	13.98%
Total capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 184,771	$ 182,541
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	$ 199,322	$ 196,916
Total capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	8.63%	8.63%
Total capital (to risk-weighted assets), For well capitalized purpose, Amount	$ 230,964	$ 228,176
Total capital (to risk-weighted assets), For well capitalized purpose, Ratio	10.00%	10.00%
Tier 1 capital (to average assets), Actual, Amount	$ 305,364	$ 304,176
Tier 1 capital (to average assets), Actual, Ratio	13.22%	13.33%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 138,578	$ 136,905
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	$ 153,129	$ 151,280
Tier 1 capital (to average assets), Required for capital1 adequacy purposes with capital buffer, Ratio	6.63%	6.63%
Tier 1 capital (to average assets), For well capitalized purpose, Amount	$ 184,771	$ 182,540
Tier 1 capital (to average assets), For well capitalized purposes, Ratio	8.00%	8.00%
Common equity tier 1 capital, Actual Amount	$ 305,364	$ 304,176
Common equity tier 1 capital, Actual Ratio	13.22%	13.33%
Common equity tier 1 capital,For capital adequacy purposes, Amount	$ 103,934	$ 102,679
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	$ 118,484	$ 117,054
Common equity tier 1 capital (to risk-weighted assets), Required for capital1 adequacy purposes with capital buffer, Ratio	5.13%	5.13%
Common equity tier 1 capital, For well capitalized purpose, Amount	$ 150,126	$ 148,314
Common equity tier 1 capital, For well capitalized purposes, Ratio	6.50%	6.50%
Tier 1 capital (to average assets), Actual, Amount	$ 305,364	$ 304,176
Tier 1 capital (to average assets), Actual, Ratio	10.13%	9.93%
Tier 1 capital (to average assets), For capital adequacy purposes, Amount	$ 120,625	$ 122,521
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	$ 120,625	$ 122,521
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	$ 150,781	$ 153,151
Tier 1 capital (to average assets), For well capitalized purposes, Ratio	5.00%	5.00%