Loans and Leases - Reserve for Loan and Lease Losses Roll Forward (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) loan borrowers	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		$ 17,628	$ 20,662	$ 24,494
Charge-offs		(6,988)	(8,496)	(8,850)
Recoveries		2,038	1,660	1,411
Provision (recovery of provision)		4,646	3,623	3,607
Provision (recovery of provision) for acquired credit impaired loans		175	179	0
Ending balance		17,499	17,628	20,662
Commercial, Financial and Agricultural [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		6,418	6,920	9,789
Charge-offs		(4,827)	(4,793)	(2,834)
Recoveries		1,454	1,032	247
Provision (recovery of provision)		3,992	3,259	(282)
Provision (recovery of provision) for acquired credit impaired loans		0	0	0
Ending balance		7,037	6,418	6,920
Real Estate-Commercial and Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		6,572	8,943	8,780
Charge-offs		(307)	(1,895)	(4,363)
Recoveries		101	200	524
Provision (recovery of provision)		961	(684)	4,002
Provision (recovery of provision) for acquired credit impaired loans		178	8	0
Ending balance		7,505	6,572	8,943
Amount of Loans Charged Off Prior to Being Transferred to Loans Held for Sale	$ 1,300
Number of Loans Charged Off Prior to Being Transferred to Loans Held for Sale | loan	2
Number of Borrowers, Loans Charged Off Prior to Being Transferred to Loans Held for Sale | borrowers	1
Real Estate-Residential Secured for Business Purpose [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		763	763	1,062
Charge-offs		(522)	(179)	(140)
Recoveries		71	28	60
Provision (recovery of provision)		462	43	(219)
Provision (recovery of provision) for acquired credit impaired loans		0	108	0
Ending balance		774	763	763
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		1,575	1,124	1,284
Charge-offs		(178)	(279)	(141)
Recoveries		88	10	34
Provision (recovery of provision)		(489)	657	(53)
Provision (recovery of provision) for acquired credit impaired loans		(3)	63	0
Ending balance		993	1,575	1,124
Loans to Individuals [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		346	360	694
Charge-offs		(395)	(549)	(796)
Recoveries		133	176	265
Provision (recovery of provision)		280	359	197
Provision (recovery of provision) for acquired credit impaired loans		0	0	0
Ending balance		364	346	360
Lease Financings [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		1,042	985	1,285
Charge-offs		(759)	(801)	(576)
Recoveries		191	214	281
Provision (recovery of provision)		314	644	(5)
Provision (recovery of provision) for acquired credit impaired loans		0	0	0
Ending balance		788	1,042	985
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		912	1,567	1,600
Provision (recovery of provision)		(874)	(655)	(33)
Provision (recovery of provision) for acquired credit impaired loans		0	0	0
Ending balance		$ 38	$ 912	$ 1,567