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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 36,604	$ 32,823	$ 35,455	$ 31,245
Charge-offs	(753)	(869)	(2,966)	(3,099)
Recoveries	396	144	982	907
Provision	1,046	1,827	3,822	4,872
Ending Balance	37,293	33,925	37,293	33,925
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	26,174	23,344	25,704	21,223
Charge-offs	(24)	(315)	(256)	(618)
Recoveries	135	26	440	390
Provision	1,361	1,673	1,758	3,733
Ending Balance	27,646	24,728	27,646	24,728
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,012	1,688	2,313	1,723
Charge-offs	(151)	(196)	(1,452)	(430)
Recoveries	177	28	273	150
Provision	(70)	572	834	649
Ending Balance	1,968	2,092	1,968	2,092
Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,264	529	630	548
Charge-offs	(368)	(87)	(463)	(250)
Recoveries	2	7	7	39
Provision	(12)	65	712	177
Ending Balance	886	514	886	514
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,585	1,754	1,557	1,964
Charge-offs	(38)	(98)	(131)	(408)
Recoveries	2	3	7	3
Provision	(62)	(90)	54	10
Ending Balance	1,487	1,569	1,487	1,569
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,063	2,596	2,731	2,352
Charge-offs	0	0	(248)	(609)
Recoveries	4	4	12	24
Provision	(166)	(135)	406	698
Ending Balance	2,901	2,465	2,901	2,465
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,506	2,912	2,520	3,435
Charge-offs	(172)	(173)	(416)	(784)
Recoveries	76	76	243	301
Provision	(5)	(258)	58	(395)
Ending Balance	$ 2,405	$ 2,557	$ 2,405	$ 2,557