Regulatory Matters - Summary of Capital Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk-weighted assets)	$ 589,047	$ 549,391
Tier 1 capital (to risk-weighted assets)	477,453	442,124
Common equity Tier 1 capital (to risk-weighted assets)	447,453	412,124
Tier 1 capital (to average assets)	$ 477,453	$ 442,124
Total capital (to risk-weighted assets), ratio	13.40%	13.48%
Tier 1 capital (to risk-weighted assets), ratio	10.87%	10.85%
Common equity Tier 1 capital (to risk-weighted assets), ratio	10.18%	10.11%
Tier 1 capital (to average assets), ratio	9.12%	9.07%
Total capital (to risk-weighted assets), For capital adequacy purposes	$ 406,477	$ 351,431
Tier 1 capital (to risk-weighted assets), For capital adequacy purposes	318,590	269,940
Common equity Tier 1 capital (to risk-weighted assets), For capital adequacy purposes	252,675	208,821
Tier 1 capital (to average assets), For capital adequacy purposes	$ 209,431	$ 194,927
Total capital (to risk-weighted assets), For capital adequacy purposes , ratio	9.00%	9.00%
Tier 1 capital (to risk-weighted assets), For capital adequacy purposes, ratio	7.00%	7.00%
Common equity Tier 1 capital (to risk-weighted assets),For capital adequacy purposes, ratio	5.80%	5.00%
Tier 1 capital (to average assets), For capital adequacy purposes, ratio	4.00%	4.00%
Subsidiaries
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk-weighted assets)	$ 563,910	$ 530,458
Tier 1 capital (to risk-weighted assets)	525,979	496,737
Common equity Tier 1 capital (to risk-weighted assets)	525,979	496,737
Tier 1 capital (to average assets)	$ 525,979	$ 496,737
Total capital (to risk-weighted assets), ratio	12.86%	13.03%
Tier 1 capital (to risk-weighted assets), ratio	12.00%	12.21%
Common equity Tier 1 capital (to risk-weighted assets), ratio	12.00%	12.21%
Tier 1 capital (to average assets), ratio	10.06%	10.21%
Total capital (to risk-weighted assets), For capital adequacy purposes	$ 405,552	$ 350,996
Tier 1 capital (to risk-weighted assets), For capital adequacy purposes	317,865	269,605
Common equity Tier 1 capital (to risk-weighted assets), For capital adequacy purposes	252,100	208,563
Tier 1 capital (to average assets), For capital adequacy purposes	$ 209,239	$ 194,691
Total capital (to risk-weighted assets), For capital adequacy purposes , ratio	9.25%	8.63%
Tier 1 capital (to risk-weighted assets), For capital adequacy purposes, ratio	7.25%	6.63%
Common equity Tier 1 capital (to risk-weighted assets),For capital adequacy purposes, ratio	5.75%	5.13%
Tier 1 capital (to average assets), For capital adequacy purposes, ratio	4.00%	4.00%
Total capital (to risk - weighted assets), To be well capitalized under prompt corrective action provisions	$ 438,435	$ 406,952
Tier 1 capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions	350,748	325,561
Common equity Tier 1 capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions	284,983	264,519
Tier 1 capital (to average assets), To be well capitalized under prompt corrective action provisions	$ 261,548	$ 243,364
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), To be well capitalized under prompt corrective action provisions, ratio	8.00%	8.00%
Common equity Tier 1 capital (to risk-weighted assets), To be well capitalized under prompt corrective action provision, ratio	6.50%	6.50%
Tier 1 capital (to average assets), To be well capitalized under prompt corrective action provisions, ratio	5.00%	5.00%

Common Equity Tier One Capital Required For Capital Adequacy To Risk Weighted Assets Amount

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Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Asset

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The amount of total capital as defined in the regulations.

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