Loans and Leases - Concessions Granted on Accruing and Nonaccrual Loans Restructured (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) loan Investment	Dec. 31, 2019 USD ($) loan Investment
Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	1
Amount	$ 0	$ 55
Accrual Troubled Debt Restructuring Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	0
Amount	$ 0	$ 0
Accrual Troubled Debt Restructuring Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	1
Amount	$ 0	$ 55
Accrual Troubled Debt Restructuring Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	0
Amount	$ 0	$ 0
Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	2	6
Amount	$ 1,163	$ 13,889
Nonaccrual Troubled Debt Restructured Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	1
Amount	$ 0	$ 19
Nonaccrual Troubled Debt Restructured Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	2	3
Amount	$ 1,163	$ 2,269
Nonaccrual Troubled Debt Restructured Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	2
Amount	$ 0	$ 11,601
Real Estate-Home Equity Secured for Personal Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		1
Amount		$ 55
Real Estate-Home Equity Secured for Personal Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		0
Amount		$ 0
Real Estate-Home Equity Secured for Personal Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		1
Amount		$ 55
Real Estate-Home Equity Secured for Personal Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		0
Amount		$ 0
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	1	4
Amount	$ 619	$ 1,475
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	1
Amount	$ 0	$ 19
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	1	2
Amount	$ 619	$ 956
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans	0	1
Amount	$ 0	$ 500
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0	2
Amount		$ 12,414
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		0
Amount		$ 0
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan		1
Amount		$ 1,313
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | Investment		1
Amount		$ 11,101
Real Estate-Residential Secured for Personal Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | Investment	0	1
Real Estate-Residential Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	1	0
Amount	$ 544
Real Estate-Residential Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0
Amount	$ 0
Real Estate-Residential Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	1
Amount	$ 544
Real Estate-Residential Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Incremental Extension of Credit [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of loans | loan	0
Amount	$ 0