Loans - Loans by Class Modified as Troubled Debt Restructurings (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	25	20
Commercial, industrial, and agricultural
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	10	11
Commercial mortgages
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	15	9
Residential real estate
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0
Consumer
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0
Credit cards
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0
Trouble Debt Restructuring
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	5	6	1
Pre-Modification Outstanding Recorded Investment \| $	$ 1,570	$ 9,171	$ 109
Post-Modification Outstanding Recorded Investment \| $	$ 1,570	$ 9,171	$ 109
Trouble Debt Restructuring \| Commercial, industrial, and agricultural
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	4	1
Pre-Modification Outstanding Recorded Investment \| $	$ 0	$ 2,750	$ 109
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 2,750	$ 109
Trouble Debt Restructuring \| Commercial mortgages
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	5	2	0
Pre-Modification Outstanding Recorded Investment \| $	$ 1,570	$ 6,421	$ 0
Post-Modification Outstanding Recorded Investment \| $	$ 1,570	$ 6,421	$ 0
Trouble Debt Restructuring \| Residential real estate
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0	0
Pre-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0
Trouble Debt Restructuring \| Consumer
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0	0
Pre-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0
Trouble Debt Restructuring \| Credit cards
Schedule Of Financial Receivables [Line Items]
Number of Loans \| loan	0	0	0
Pre-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 0	$ 0

Schedule Of Financial Receivables [Line Items]

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- Definition

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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+ References

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