Loans and Leases - Concessions Granted on Accruing and Nonaccrual Loans Restructured (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	3	2
Amount | $	$ 9,206	$ 1,960
Accrual Troubled Debt Restructuring Loans [Member] | Interest Only Terms Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0	1
Amount | $	$ 0	$ 415
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	3	1
Amount | $	$ 9,206	$ 1,545
Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	3	3
Amount | $	$ 1,455	$ 498
Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms Extension [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] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	1	3
Amount | $	$ 328	$ 498
Nonaccrual Troubled Debt Restructured Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	2	0
Amount | $	$ 1,127	$ 0
Commercial, Financial and Agricultural [Member] | Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0	1
Amount | $		$ 1,545
Commercial, Financial and Agricultural [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Interest Only Terms Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan		0
Amount | $		$ 0
Commercial, Financial and Agricultural [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
Commercial, Financial and Agricultural [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 | $		$ 1,545
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	2	0
Amount | $	$ 1,127
Commercial, Financial and Agricultural [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms Extension [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] | Maturity Date Extension [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] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	2
Amount | $	$ 1,127
Real Estate-Commercial [Member] | Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	3	0
Amount | $	$ 9,206
Real Estate-Commercial [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Interest Only Terms Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0
Amount | $	$ 0
Real Estate-Commercial [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-Commercial [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Amortization Period Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	3
Amount | $	$ 9,206
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	1	0
Amount | $	$ 328
Real Estate-Commercial [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms 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] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	1
Amount | $	$ 328
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	0
Amount | $	$ 0
Real Estate-Residential Secured for Business Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0	1
Amount | $		$ 415
Real Estate-Residential Secured for Business Purpose [Member] | Accrual Troubled Debt Restructuring Loans [Member] | Interest Only Terms Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan		1
Amount | $		$ 415
Real Estate-Residential Secured for Business 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-Residential Secured for Business 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		0
Amount | $		$ 0
Real Estate-Residential Secured for Business Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0	1
Amount | $		$ 312
Real Estate-Residential Secured for Business Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan		0
Amount | $		$ 0
Real Estate-Residential Secured for Business 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		1
Amount | $		$ 312
Real Estate-Residential Secured for Business 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		0
Amount | $		$ 0
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	0	1
Amount | $		$ 34
Real Estate-Residential Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms 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] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan		1
Amount | $		$ 34
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		0
Amount | $		$ 0
Real Estate-Home Equity Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan	0	1
Amount | $		$ 152
Real Estate-Home Equity Secured for Personal Purpose [Member] | Nonaccrual Troubled Debt Restructured Loans [Member] | Interest Only Terms 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] | Nonaccrual Troubled Debt Restructured Loans [Member] | Maturity Date Extension [Member]
Concessions granted on accruing and non-accrual loans restructured
No. of Loans | loan		1
Amount | $		$ 152
Real Estate-Home Equity 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		0
Amount | $		$ 0