Loans, Leases and Other Real Estate - Impaired Loans with and without Specific Allowances (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Recorded Investment in Impaired Loans	$ 19,304	$ 22,591
Contractual Unpaid Principal Balance	20,140	23,461
Related Allowance	865	505
Average Investment in Impaired Loans	20,245	23,236
Interest Income Recognized	308	705
Commercial, secured by real estate
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	7,398	12,155
Loans with related allowance, Recorded Investment in Impaired Loans	7,787	5,381
Recorded Investment in Impaired Loans	15,185	17,536
Loans without related allowance, Contractual Unpaid Principal Balance	7,715	12,497
Loans with related allowance, Contractual Unpaid Principal Balance	8,129	5,721
Contractual Unpaid Principal Balance	15,844	18,218
Related Allowance	452	454
Loans without related allowance, Average Investment in Impaired Loans	6,730	12,774
Loans with related allowance, Average Investment in Impaired Loans	8,178	5,029
Average Investment in Impaired Loans	14,908	17,803
Loans without related allowance, Interest Income Recognized	89	366
Loans with related allowance, Interest Income Recognized	172	206
Interest Income Recognized	261	572
Commercial, industrial and other
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	1,525	618
Loans with related allowance, Recorded Investment in Impaired Loans	228	164
Recorded Investment in Impaired Loans	1,753	782
Loans without related allowance, Contractual Unpaid Principal Balance	1,526	618
Loans with related allowance, Contractual Unpaid Principal Balance	228	164
Contractual Unpaid Principal Balance	1,754	782
Related Allowance	8	9
Loans without related allowance, Average Investment in Impaired Loans	1,381	618
Loans with related allowance, Average Investment in Impaired Loans	228	283
Average Investment in Impaired Loans	1,609	901
Loans without related allowance, Interest Income Recognized	10	25
Loans with related allowance, Interest Income Recognized	6	14
Interest Income Recognized	16	39
Leases
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	0
Loans with related allowance, Recorded Investment in Impaired Loans	663	65
Recorded Investment in Impaired Loans	663	65
Loans without related allowance, Contractual Unpaid Principal Balance	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	663	65
Contractual Unpaid Principal Balance	663	65
Related Allowance	393	30
Loans without related allowance, Average Investment in Impaired Loans	0	0
Loans with related allowance, Average Investment in Impaired Loans	279	29
Average Investment in Impaired Loans	279	29
Loans without related allowance, Interest Income Recognized	0	0
Loans with related allowance, Interest Income Recognized	0	0
Interest Income Recognized	0	0
Real estate - residential mortgage
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	963
Loans with related allowance, Recorded Investment in Impaired Loans	757	781
Recorded Investment in Impaired Loans	757	1,744
Loans without related allowance, Contractual Unpaid Principal Balance	0	980
Loans with related allowance, Contractual Unpaid Principal Balance	902	919
Contractual Unpaid Principal Balance	902	1,899
Related Allowance	4	4
Loans without related allowance, Average Investment in Impaired Loans	478	996
Loans with related allowance, Average Investment in Impaired Loans	557	940
Average Investment in Impaired Loans	1,035	1,936
Loans without related allowance, Interest Income Recognized	4	15
Loans with related allowance, Interest Income Recognized	10	27
Interest Income Recognized	14	42
Real estate - construction
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	1,471
Loans with related allowance, Recorded Investment in Impaired Loans	0	0
Recorded Investment in Impaired Loans	0	1,471
Loans without related allowance, Contractual Unpaid Principal Balance	0	1,471
Loans with related allowance, Contractual Unpaid Principal Balance	0	0
Contractual Unpaid Principal Balance	0	1,471
Related Allowance	0	0
Loans without related allowance, Average Investment in Impaired Loans	1,463	1,471
Loans with related allowance, Average Investment in Impaired Loans	0	0
Average Investment in Impaired Loans	1,463	1,471
Loans without related allowance, Interest Income Recognized	0	0
Loans with related allowance, Interest Income Recognized	0	0
Interest Income Recognized	0	0
Home equity and consumer
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	0
Loans with related allowance, Recorded Investment in Impaired Loans	946	993
Recorded Investment in Impaired Loans	946	993
Loans without related allowance, Contractual Unpaid Principal Balance	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	977	1,026
Contractual Unpaid Principal Balance	977	1,026
Related Allowance	8	8
Loans without related allowance, Average Investment in Impaired Loans	0	6
Loans with related allowance, Average Investment in Impaired Loans	951	1,090
Average Investment in Impaired Loans	951	1,096
Loans without related allowance, Interest Income Recognized	0	0
Loans with related allowance, Interest Income Recognized	17	52
Interest Income Recognized	$ 17	$ 52

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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