Loans and Other Real Estate - Impaired Loans with and without Specific Allowances (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Recorded Investment in Impaired Loans	$ 20,236	$ 19,702
Contractual Unpaid Principal Balance	22,024	21,360
Related Allowance	259	338
Average Investment in Impaired Loans	18,603	20,012
Interest Income Recognized	144	592
Commercial, secured by real estate
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	12,188	9,284
Loans with related allowance, Recorded Investment in Impaired Loans	3,797	7,270
Recorded Investment in Impaired Loans	15,985	16,554
Loans without related allowance, Contractual Unpaid Principal Balance	12,883	9,829
Loans with related allowance, Contractual Unpaid Principal Balance	4,070	7,597
Contractual Unpaid Principal Balance	16,953	17,426
Related Allowance	229	307
Loans without related allowance, Average Investment in Impaired Loans	8,878	7,369
Loans with related allowance, Average Investment in Impaired Loans	6,642	7,594
Average Investment in Impaired Loans	15,520	14,963
Loans without related allowance, Interest Income Recognized	52	188
Loans with related allowance, Interest Income Recognized	72	317
Interest Income Recognized	124	505
Commercial, industrial and other
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	2,309	1,151
Loans with related allowance, Recorded Investment in Impaired Loans	200	209
Recorded Investment in Impaired Loans	2,509	1,360
Loans without related allowance, Contractual Unpaid Principal Balance	2,633	1,449
Loans with related allowance, Contractual Unpaid Principal Balance	199	209
Contractual Unpaid Principal Balance	2,832	1,658
Related Allowance	8	7
Loans without related allowance, Average Investment in Impaired Loans	1,142	1,834
Loans with related allowance, Average Investment in Impaired Loans	199	209
Average Investment in Impaired Loans	1,341	2,043
Loans without related allowance, Interest Income Recognized	4	19
Loans with related allowance, Interest Income Recognized	3	12
Interest Income Recognized	7	31
Equipment finance
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	301	301
Loans with related allowance, Recorded Investment in Impaired Loans	26	30
Recorded Investment in Impaired Loans	327	331
Loans without related allowance, Contractual Unpaid Principal Balance	597	597
Loans with related allowance, Contractual Unpaid Principal Balance	26	30
Contractual Unpaid Principal Balance	623	627
Related Allowance	12	14
Loans without related allowance, Average Investment in Impaired Loans	301	376
Loans with related allowance, Average Investment in Impaired Loans	26	19
Average Investment in Impaired Loans	327	395
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	0
Loans with related allowance, Recorded Investment in Impaired Loans	715	730
Recorded Investment in Impaired Loans	715	730
Loans without related allowance, Contractual Unpaid Principal Balance	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	875	884
Contractual Unpaid Principal Balance	875	884
Related Allowance	4	4
Loans without related allowance, Average Investment in Impaired Loans	0	242
Loans with related allowance, Average Investment in Impaired Loans	718	745
Average Investment in Impaired Loans	718	987
Loans without related allowance, Interest Income Recognized	0	4
Loans with related allowance, Interest Income Recognized	5	20
Interest Income Recognized	5	24
Real estate - construction
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	0	0
Recorded Investment in Impaired Loans	0	0
Loans without related allowance, Contractual Unpaid Principal Balance	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	0	0
Contractual Unpaid Principal Balance	0	0
Related Allowance	0	0
Loans without related allowance, Average Investment in Impaired Loans	0	726
Loans with related allowance, Average Investment in Impaired Loans	0	0
Average Investment in Impaired Loans	0	726
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	700	727
Recorded Investment in Impaired Loans	700	727
Loans without related allowance, Contractual Unpaid Principal Balance	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	741	765
Contractual Unpaid Principal Balance	741	765
Related Allowance	6	6
Loans without related allowance, Average Investment in Impaired Loans	0	0
Loans with related allowance, Average Investment in Impaired Loans	697	898
Average Investment in Impaired Loans	697	898
Loans without related allowance, Interest Income Recognized	0	0
Loans with related allowance, Interest Income Recognized	8	32
Interest Income Recognized	$ 8	$ 32

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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