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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 48,884	$ 37,979	$ 40,003	$ 37,688
Charge-offs	(141)	(413)	(624)	(929)
Recoveries	96	1,096	237	1,395
Provision	9,000	0	18,223	508
Ending Balance	57,839	38,662	57,839	38,662
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	34,793	27,515	28,950	27,881
Charge-offs	0	0	(169)	(187)
Recoveries	21	25	47	140
Provision	8,466	555	14,452	261
Ending Balance	43,280	28,095	43,280	28,095
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	5,489	2,592	3,289	1,742
Charge-offs	0	(38)	0	(185)
Recoveries	13	947	43	1,044
Provision	(804)	(868)	1,366	32
Ending Balance	4,698	2,633	4,698	2,633
Equipment finance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,257	947	957	987
Charge-offs	(14)	(293)	(98)	(380)
Recoveries	24	0	38	2
Provision	1,704	401	2,074	446
Ending Balance	2,971	1,055	2,971	1,055
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,600	1,564	1,725	1,566
Charge-offs	0	0	(116)	(50)
Recoveries	0	2	20	11
Provision	(164)	40	(193)	79
Ending Balance	1,436	1,606	1,436	1,606
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,344	2,887	2,672	3,015
Charge-offs	0	0	0	0
Recoveries	16	60	48	65
Provision	(241)	(239)	399	(372)
Ending Balance	3,119	2,708	3,119	2,708
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,401	2,474	2,410	2,497
Charge-offs	(127)	(82)	(241)	(127)
Recoveries	22	62	41	133
Provision	39	111	125	62
Ending Balance	$ 2,335	$ 2,565	$ 2,335	$ 2,565