Loans 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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 37,979	$ 35,644	$ 37,688	$ 35,455
Charge-offs	(413)	(963)	(929)	(2,213)
Recoveries	1,096	431	1,395	586
Provision	0	1,492	508	2,776
Ending Balance	38,662	36,604	38,662	36,604
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	27,515	25,817	27,881	25,704
Charge-offs	0	(210)	(187)	(232)
Recoveries	25	274	140	305
Provision	555	293	261	397
Ending Balance	28,095	26,174	28,095	26,174
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,592	1,768	1,742	2,313
Charge-offs	(38)	(289)	(185)	(1,301)
Recoveries	947	76	1,044	96
Provision	(868)	457	32	904
Ending Balance	2,633	2,012	2,633	2,012
Equipment finance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	947	1,042	987	630
Charge-offs	(293)	(72)	(380)	(95)
Recoveries	0	3	2	5
Provision	401	291	446	724
Ending Balance	1,055	1,264	1,055	1,264
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,564	1,589	1,566	1,557
Charge-offs	0	0	(50)	(93)
Recoveries	2	3	11	5
Provision	40	(7)	79	116
Ending Balance	1,606	1,585	1,606	1,585
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,887	2,932	3,015	2,731
Charge-offs	0	(248)	0	(248)
Recoveries	60	3	65	8
Provision	(239)	376	(372)	572
Ending Balance	2,708	3,063	2,708	3,063
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,474	2,496	2,497	2,520
Charge-offs	(82)	(144)	(127)	(244)
Recoveries	62	72	133	167
Provision	111	82	62	63
Ending Balance	$ 2,565	$ 2,506	$ 2,565	$ 2,506