Loans, Leases and Other Real Estate - Impaired Loans with and without Specific Allowances (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment in Impaired Loans	$ 21,590	$ 25,285
Contractual Unpaid Principal Balance	22,374	27,356
Related Allowance	504	529
Average Investment in Impaired Loans	24,093	26,675
Interest Income Recognized	515	648
Commercial, Secured by Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	10,852	12,764
Loans with related allowance, Recorded Investment in Impaired Loans	5,425	5,860
Recorded Investment in Impaired Loans	16,277	18,624
Loans without related allowance, Contractual Unpaid Principal Balance	11,125	13,195
Loans with related allowance, Contractual Unpaid Principal Balance	5,757	6,142
Contractual Unpaid Principal Balance	16,882	19,337
Related Allowance	480	392
Loans without related allowance, Average Investment in Impaired Loans	13,491	13,631
Loans with related allowance, Average Investment in Impaired Loans	5,030	6,549
Average Investment in Impaired Loans	18,521	20,180
Loans without related allowance, Interest Income Recognized	259	229
Loans with related allowance, Interest Income Recognized	151	273
Interest Income Recognized	410	502
Commercial, Industrial and Other [Member]
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	635	603
Loans with related allowance, Recorded Investment in Impaired Loans	169	349
Recorded Investment in Impaired Loans	804	952
Loans without related allowance, Contractual Unpaid Principal Balance	635	603
Loans with related allowance, Contractual Unpaid Principal Balance	169	349
Contractual Unpaid Principal Balance	804	952
Related Allowance	10	12
Loans without related allowance, Average Investment in Impaired Loans	635	1,109
Loans with related allowance, Average Investment in Impaired Loans	328	360
Average Investment in Impaired Loans	963	1,469
Loans without related allowance, Interest Income Recognized	19	24
Loans with related allowance, Interest Income Recognized	12	17
Interest Income Recognized	31	41
Leases [Member]
Financing Receivable, Impaired [Line Items]
Loans with related allowance, Average Investment in Impaired Loans		1
Average Investment in Impaired Loans		1
Real Estate - Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	967	1,880
Loans with related allowance, Recorded Investment in Impaired Loans	992	1,031
Recorded Investment in Impaired Loans	1,959	2,911
Loans without related allowance, Contractual Unpaid Principal Balance	984	3,146
Loans with related allowance, Contractual Unpaid Principal Balance	1,125	1,100
Contractual Unpaid Principal Balance	2,109	4,246
Related Allowance	5	31
Loans without related allowance, Average Investment in Impaired Loans	1,011	2,430
Loans with related allowance, Average Investment in Impaired Loans	1,006	1,011
Average Investment in Impaired Loans	2,017	3,441
Loans without related allowance, Interest Income Recognized	12	16
Loans with related allowance, Interest Income Recognized	22	30
Interest Income Recognized	34	46
Real Estate-Construction [Member]
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	1,472	1,471
Recorded Investment in Impaired Loans	1,472	1,471
Loans without related allowance, Contractual Unpaid Principal Balance	1,472	1,471
Contractual Unpaid Principal Balance	1,472	1,471
Loans without related allowance, Average Investment in Impaired Loans	1,472	12
Average Investment in Impaired Loans	1,472	12
Home Equity and Consumer [Member]
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans		139
Loans with related allowance, Recorded Investment in Impaired Loans	1,078	1,188
Recorded Investment in Impaired Loans	1,078	1,327
Loans without related allowance, Contractual Unpaid Principal Balance		139
Loans with related allowance, Contractual Unpaid Principal Balance	1,107	1,211
Contractual Unpaid Principal Balance	1,107	1,350
Related Allowance	9	94
Loans without related allowance, Average Investment in Impaired Loans		388
Loans with related allowance, Average Investment in Impaired Loans	1,120	1,184
Average Investment in Impaired Loans	1,120	1,572
Loans with related allowance, Interest Income Recognized	40	59
Interest Income Recognized	$ 40	$ 59

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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