Loans and the Allowance for Credit Losses - Recorded Investment in Non-Accrual Loans and TDRs (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Non-accrual loans	$ 36,212	$ 36,880
TDRs	7,463	5,755
Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	5,799	3,927
Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,664	1,828
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	4,572	3,302
TDRs	97	111
Commercial and Industrial [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	97	111
Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	5,370	5,345
TDRs	656	663
Home Equity [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	396	363
Home Equity [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	260	300
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	8,412	9,963
TDRs	566	820
Commercial Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	418	655
Commercial Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	148	165
Commercial Real Estate [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	74	469
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	8,338	9,494
TDRs	566	820
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	418	655
Commercial Real Estate [Member] | Commercial Real Estate - Improved Property [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	148	165
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	17,567	17,925
TDRs	6,131	4,133
Residential Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	4,876	2,779
Residential Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,255	1,354
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	291	345
TDRs	13	28
Consumer [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	12	19
Consumer [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	$ 1	$ 9