Loans - Investment in Loans by Portfolio Segment and Based on Impairment (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	$ 20,443	$ 21,202
Provision (recovery) for loan losses	61	407
Charge-offs	(433)	(271)
Recoveries	375	272
Allowance, Ending balance	20,446	21,610
Allowance, Loans individually evaluated for impairment	1,216	1,821	$ 1,201
Allowance, Loans collectively evaluated for impairment	19,230		19,242
Period-end balances, Loans individually evaluated for impairment	21,166		20,594
Period-end balances, Loans collectively evaluated for impairment	2,208,191		2,170,068
Total loans	2,229,357		2,190,662
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	11,875	12,542
Provision (recovery) for loan losses	181	396
Charge-offs	(88)
Recoveries	146	157
Allowance, Ending balance	12,114	13,095
Allowance, Loans individually evaluated for impairment	139	516	103
Allowance, Loans collectively evaluated for impairment	11,975		11,772
Period-end balances, Loans individually evaluated for impairment	3,276		2,017
Period-end balances, Loans collectively evaluated for impairment	971,395		940,914
Total loans	974,671		942,931
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	5,923	5,860
Provision (recovery) for loan losses	(178)	(93)
Charge-offs	(20)	(85)
Recoveries	98	19
Allowance, Ending balance	5,823	5,701
Allowance, Loans individually evaluated for impairment	782	967	798
Allowance, Loans collectively evaluated for impairment	5,041		5,125
Period-end balances, Loans individually evaluated for impairment	12,759		13,086
Period-end balances, Loans collectively evaluated for impairment	966,929		957,604
Total loans	979,688		970,690
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	2,645	2,800
Provision (recovery) for loan losses	58	104
Charge-offs	(325)	(186)
Recoveries	131	96
Allowance, Ending balance	2,509	2,814
Allowance, Loans individually evaluated for impairment	295	$ 338	300
Allowance, Loans collectively evaluated for impairment	2,214		2,345
Period-end balances, Loans individually evaluated for impairment	5,131		5,491
Period-end balances, Loans collectively evaluated for impairment	269,867		271,550
Total loans	$ 274,998		$ 277,041

Loans and leases receivable gross carrying amount before loan allowances and deferred loan costs.

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- Definition

Provision for (recovery) of loan losses.

+ References

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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- Definition

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

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- Definition

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.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of direct write-downs of financing receivables charged against the allowance.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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