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
	Mar. 31, 2018	Mar. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 35,455	$ 31,245
Charge-offs	(1,250)	(1,360)
Recoveries	155	487
Provision	1,284	1,218
Ending Balance	35,644	31,590
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	25,704	21,223
Charge-offs	(22)	(220)
Recoveries	31	219
Provision	104	861
Ending Balance	25,817	22,083
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,313	1,723
Charge-offs	(1,012)	(163)
Recoveries	20	95
Provision	447	137
Ending Balance	1,768	1,792
Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	630	548
Charge-offs	(23)	(43)
Recoveries	2	4
Provision	433	(7)
Ending Balance	1,042	502
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,557	1,964
Charge-offs	(93)	(141)
Recoveries	2	0
Provision	123	2
Ending Balance	1,589	1,825
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,731	2,352
Charge-offs	0	(609)
Recoveries	5	15
Provision	196	620
Ending Balance	2,932	2,378
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,520	3,435
Charge-offs	(100)	(184)
Recoveries	95	154
Provision	(19)	(395)
Ending Balance	$ 2,496	$ 3,010