Loans and Allowance for Credit Losses - Schedule of Activity in Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	$ 28,674	$ 46,343	$ 31,738	$ 43,710
(Charge-offs)/ Recoveries	53	(85)	(1,907)	(172)
(Payments)/ Disbursements	(1,118)	(16,961)	(2,222)	(19,751)
Additions	0	14,534	0	20,044
Ending Balance	27,609	43,831	27,609	43,831
Commercial
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	10,928	11,646	12,412	10,275
(Charge-offs)/ Recoveries	0	(93)	(694)	(100)
(Payments)/ Disbursements	(330)	25	(1,120)	(1,004)
Additions	0	7,294	0	9,701
Ending Balance	10,598	18,872	10,598	18,872
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	12,848	29,137	14,277	27,671
(Charge-offs)/ Recoveries	19	4	(1,253)	(71)
(Payments)/ Disbursements	(161)	(16,702)	(318)	(18,264)
Additions	0	6,924	0	10,027
Ending Balance	12,706	19,363	12,706	19,363
BBCC
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	562		578
(Charge-offs)/ Recoveries	31		31
(Payments)/ Disbursements	(446)		(462)
Additions	0		0
Ending Balance	147		147
Residential real estate
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	3,040	3,247	3,107	3,390
(Charge-offs)/ Recoveries	0	0	0	0
(Payments)/ Disbursements	(28)	(167)	(95)	(310)
Additions	0	0	0	0
Ending Balance	3,012	3,080	3,012	3,080
Indirect
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	0		0
(Charge-offs)/ Recoveries	2		5
(Payments)/ Disbursements	(2)		(5)
Additions	0		0
Ending Balance	0		0
Direct
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	922		983
(Charge-offs)/ Recoveries	0		2
(Payments)/ Disbursements	(143)		(206)
Additions	0		0
Ending Balance	779		779
Home equity
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance	374		381
(Charge-offs)/ Recoveries	1		2
(Payments)/ Disbursements	(8)		(16)
Additions	0		0
Ending Balance	$ 367		$ 367
Consumer
Financing Receivable, Troubled Debt Restructuring [Roll Forward]
Beginning Balance		2,313		2,374
(Charge-offs)/ Recoveries		4		(1)
(Payments)/ Disbursements		(117)		(173)
Additions		316		316
Ending Balance		$ 2,516		$ 2,516