Loans and the Allowance for Credit Losses - Recorded Investment in Non-Accrual Loans and TDRs (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Non-accrual loans	$ 34,575	$ 36,880
TDRs	5,331	5,755
Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	3,563	3,927
Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,768	1,828
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	1,571	3,302
TDRs	104	111
Commercial and Industrial [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	104	111
Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	5,181	5,345
TDRs	641	663
Home Equity [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	388	363
Home Equity [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	253	300
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	9,127	9,963
TDRs	583	820
Commercial Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	426	655
Commercial Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	157	165
Commercial Real Estate [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	120	469
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	9,007	9,494
TDRs	583	820
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	426	655
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	157	165
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	18,358	17,925
TDRs	3,985	4,133
Residential Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	2,632	2,779
Residential Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,353	1,354
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	338	345
TDRs	18	28
Consumer [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	13	19
Consumer [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	$ 5	$ 9