Loans - Investment in Loans by Portfolio Segment and Based on Impairment (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	$ 20,446	$ 21,610	$ 20,443	$ 21,202
Provision (recovery) for loan losses	(51)	(138)	10	269
Charge-offs	(194)	(254)	(627)	(525)
Recoveries	281	187	656	459
Allowance, Ending balance	20,482	21,405	20,482	21,405
Allowance, Loans individually evaluated for impairment	1,816	1,661	1,816	1,661	$ 1,201
Allowance, Loans collectively evaluated for impairment	18,666		18,666		19,242
Period-end balances, Loans individually evaluated for impairment	25,139		25,139		20,594
Period-end balances, Loans collectively evaluated for impairment	2,217,592		2,217,592		2,170,068
Total loans	2,242,731		2,242,731		2,190,662
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	12,114	13,095	11,875	12,542
Provision (recovery) for loan losses	263	(263)	444	133
Charge-offs		(75)	(88)	(75)
Recoveries	170	51	316	208
Allowance, Ending balance	12,547	12,808	12,547	12,808
Allowance, Loans individually evaluated for impairment	857	514	857	514	103
Allowance, Loans collectively evaluated for impairment	11,690		11,690		11,772
Period-end balances, Loans individually evaluated for impairment	7,680		7,680		2,017
Period-end balances, Loans collectively evaluated for impairment	966,626		966,626		940,914
Total loans	974,306		974,306		942,931
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	5,823	5,701	5,923	5,860
Provision (recovery) for loan losses	(312)	180	(490)	87
Charge-offs	(79)	(96)	(99)	(181)
Recoveries	26	82	124	101
Allowance, Ending balance	5,458	5,867	5,458	5,867
Allowance, Loans individually evaluated for impairment	669	834	669	834	798
Allowance, Loans collectively evaluated for impairment	4,789		4,789		5,125
Period-end balances, Loans individually evaluated for impairment	12,402		12,402		13,086
Period-end balances, Loans collectively evaluated for impairment	976,492		976,492		957,604
Total loans	988,894		988,894		970,690
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	2,509	2,814	2,645	2,800
Provision (recovery) for loan losses	(2)	(55)	56	49
Charge-offs	(115)	(83)	(440)	(269)
Recoveries	85	54	216	150
Allowance, Ending balance	2,477	2,730	2,477	2,730
Allowance, Loans individually evaluated for impairment	290	$ 313	290	$ 313	300
Allowance, Loans collectively evaluated for impairment	2,187		2,187		2,345
Period-end balances, Loans individually evaluated for impairment	5,057		5,057		5,491
Period-end balances, Loans collectively evaluated for impairment	274,474		274,474		271,550
Total loans	$ 279,531		$ 279,531		$ 277,041

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

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Provision for (recovery) of loan losses.

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

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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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The balance of financing receivables that were collectively 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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