Loans and the Allowance for Credit Losses - Loans Identified as TDRs (Detail) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) Contract	Jun. 30, 2017 USD ($) Contract	Jun. 30, 2018 USD ($) Contract	Jun. 30, 2017 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Number of Modifications \| Contract	4	4	11	8
Pre-Modification Outstanding Recorded Investment	$ 68	$ 77	$ 278	$ 226
Post-Modification Outstanding Recorded Investment	$ 65	$ 74	$ 252	$ 211
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications \| Contract	1		1	2
Pre-Modification Outstanding Recorded Investment	$ 9		$ 10	$ 125
Post-Modification Outstanding Recorded Investment	$ 9		$ 9	$ 120
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications \| Contract		1	5	2
Pre-Modification Outstanding Recorded Investment		$ 11	$ 203	$ 22
Post-Modification Outstanding Recorded Investment		$ 10	$ 185	$ 18
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications \| Contract	2	2	4	3
Pre-Modification Outstanding Recorded Investment	$ 39	$ 22	$ 45	$ 34
Post-Modification Outstanding Recorded Investment	$ 36	$ 20	$ 38	$ 29
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications \| Contract	1	1	1	1
Pre-Modification Outstanding Recorded Investment	$ 20	$ 44	$ 20	$ 45
Post-Modification Outstanding Recorded Investment	$ 20	$ 44	$ 20	$ 44

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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