Loans and Leases - Average Recorded Investment in Impaired Loans and Leases and Analysis of Interest on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 29,405	$ 30,215	$ 35,584
Interest income recognized	25	382	1,060
Additional interest income that would have been recognized under original terms	1,795	1,703	889
Commercial, Financial and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	2,826	6,242	10,456
Interest income recognized	17	134	200
Additional interest income that would have been recognized under original terms	222	335	347
Real Estate-Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	21,068	19,665	20,054
Interest income recognized	4	222	792
Additional interest income that would have been recognized under original terms	1,169	1,073	289
Real Estate-Construction [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	176	123	253
Interest income recognized	0	0	0
Additional interest income that would have been recognized under original terms	15	8	19
Real Estate-Residential Secured for Business Purpose [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,985	1,844	3,801
Interest income recognized	2	22	65
Additional interest income that would have been recognized under original terms	194	108	169
Real Estate-Residential Secured for Personal Purpose [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,973	1,229	614
Interest income recognized	0	3	3
Additional interest income that would have been recognized under original terms	115	94	39
Real Estate-Home Equity Secured for Personal Purpose [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,377	1,112	406
Interest income recognized	2	1	0
Additional interest income that would have been recognized under original terms	$ 80	$ 85	$ 26