Loans 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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 57,839	$ 38,662	$ 40,003	$ 37,688
Charge-offs	(682)	(809)	(1,306)	(1,738)
Recoveries	85	266	322	1,661
Provision	8,000	536	26,223	1,044
Ending Balance	65,242	38,655	65,242	38,655
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	43,280	28,095	28,950	27,881
Charge-offs	(329)	(314)	(498)	(501)
Recoveries	10	72	57	212
Provision	7,305	672	21,757	933
Ending Balance	50,266	28,525	50,266	28,525
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,698	2,633	3,289	1,742
Charge-offs	(204)	(425)	(204)	(610)
Recoveries	31	32	74	1,076
Provision	460	218	1,826	250
Ending Balance	4,985	2,458	4,985	2,458
Equipment finance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,971	1,055	957	987
Charge-offs	(96)	0	(194)	(380)
Recoveries	1	0	39	2
Provision	8	55	2,082	501
Ending Balance	2,884	1,110	2,884	1,110
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1,436	1,606	1,725	1,566
Charge-offs	0	0	(116)	(50)
Recoveries	1	55	21	66
Provision	256	(57)	63	22
Ending Balance	1,693	1,604	1,693	1,604
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,119	2,708	2,672	3,015
Charge-offs	0	0	0	0
Recoveries	21	39	69	104
Provision	(37)	(186)	362	(558)
Ending Balance	3,103	2,561	3,103	2,561
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,335	2,565	2,410	2,497
Charge-offs	(53)	(70)	(294)	(197)
Recoveries	21	68	62	201
Provision	8	(166)	133	(104)
Ending Balance	$ 2,311	$ 2,397	$ 2,311	$ 2,397