Loans, Leases and Other Real Estate - Activity in the Allowance for Loan and Lease Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 35,644	$ 31,590	$ 35,455	$ 31,245
Charge-offs	(963)	(870)	(2,213)	(2,230)
Recoveries	431	276	586	763
Provision	1,492	1,827	2,776	3,045
Ending Balance	36,604	32,823	36,604	32,823
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	25,817	22,083	25,704	21,223
Charge-offs	(210)	(83)	(232)	(303)
Recoveries	274	145	305	364
Provision	293	1,199	397	2,060
Ending Balance	26,174	23,344	26,174	23,344
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,768	1,792	2,313	1,723
Charge-offs	(289)	(71)	(1,301)	(234)
Recoveries	76	27	96	122
Provision	457	(60)	904	77
Ending Balance	2,012	1,688	2,012	1,688
Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,042	502	630	548
Charge-offs	(72)	(120)	(95)	(163)
Recoveries	3	28	5	32
Provision	291	119	724	112
Ending Balance	1,264	529	1,264	529
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,589	1,825	1,557	1,964
Charge-offs	0	(169)	(93)	(310)
Recoveries	3	0	5	0
Provision	(7)	98	116	100
Ending Balance	1,585	1,754	1,585	1,754
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,932	2,378	2,731	2,352
Charge-offs	(248)	0	(248)	(609)
Recoveries	3	5	8	20
Provision	376	213	572	833
Ending Balance	3,063	2,596	3,063	2,596
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,496	3,010	2,520	3,435
Charge-offs	(144)	(427)	(244)	(611)
Recoveries	72	71	167	225
Provision	82	258	63	(137)
Ending Balance	$ 2,506	$ 2,912	$ 2,506	$ 2,912