Loans and Other Real Estate - Allowance for Loan and Lease Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 5,855,024		$ 5,140,940
Ending Balance: Individually evaluated for impairment	223		352
Ending Balance	65,242	$ 57,839	40,003	$ 38,655	$ 38,662	$ 37,688
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,049,331		3,589,593
Ending Balance: Individually evaluated for impairment	207		228
Ending Balance	50,266	43,280	28,950	28,525	28,095	27,881
Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	751,936
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	426,821		431,934
Ending Balance: Individually evaluated for impairment	4		5
Ending Balance	4,985	4,698	3,289	2,458	2,633	1,742
Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	116,410		111,076
Ending Balance: Individually evaluated for impairment	6		10
Ending Balance	2,884	2,971	957	1,110	1,055	987
Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	342,583		335,191
Ending Balance: Individually evaluated for impairment	2		104
Ending Balance	1,693	1,436	1,725	1,604	1,606	1,566
Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	276,743		335,169
Ending Balance: Individually evaluated for impairment	0		0
Ending Balance	3,103	3,119	2,672	2,561	2,708	3,015
Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	318,021		337,977
Ending Balance: Individually evaluated for impairment	4		5
Ending Balance	2,311	$ 2,335	2,410	$ 2,397	$ 2,565	$ 2,497
Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	32,449		22,124
Ending Balance: Collectively evaluated for impairment	5,814,811		5,110,068
Ending Balance: Loans acquired with deteriorated credit quality	7,764		8,748
Total loans	5,855,024		5,140,940
Ending Balance: Individually evaluated for impairment	223		352
Ending Balance: Collectively evaluated for impairment	65,019		39,651
Ending Balance	65,242		40,003
Loans and Leases | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	27,579		15,948
Ending Balance: Collectively evaluated for impairment	4,016,426		3,567,540
Ending Balance: Loans acquired with deteriorated credit quality	5,326		6,105
Total loans	4,049,331		3,589,593
Ending Balance: Individually evaluated for impairment	207		228
Ending Balance: Collectively evaluated for impairment	50,059		28,722
Ending Balance	50,266		28,950
Loans and Leases | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	1,726
Ending Balance: Collectively evaluated for impairment	749,452
Ending Balance: Loans acquired with deteriorated credit quality	758
Total loans	751,936
Loans and Leases | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment			1,504
Ending Balance: Collectively evaluated for impairment			429,486
Ending Balance: Loans acquired with deteriorated credit quality			944
Total loans			431,934
Ending Balance: Individually evaluated for impairment	4		5
Ending Balance: Collectively evaluated for impairment	4,981		3,284
Ending Balance	4,985		3,289
Loans and Leases | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	15		23
Ending Balance: Collectively evaluated for impairment	116,395		111,053
Ending Balance: Loans acquired with deteriorated credit quality	0		0
Total loans	116,410		111,076
Ending Balance: Individually evaluated for impairment	6		10
Ending Balance: Collectively evaluated for impairment	2,878		947
Ending Balance	2,884		957
Loans and Leases | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	1,840		2,315
Ending Balance: Collectively evaluated for impairment	340,324		332,486
Ending Balance: Loans acquired with deteriorated credit quality	419		390
Total loans	342,583		335,191
Ending Balance: Individually evaluated for impairment	2		104
Ending Balance: Collectively evaluated for impairment	1,691		1,621
Ending Balance	1,693		1,725
Loans and Leases | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	694		1,663
Ending Balance: Collectively evaluated for impairment	275,291		332,722
Ending Balance: Loans acquired with deteriorated credit quality	758		784
Total loans	276,743		335,169
Ending Balance: Individually evaluated for impairment	0		0
Ending Balance: Collectively evaluated for impairment	3,103		2,672
Ending Balance	3,103		2,672
Loans and Leases | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	595		671
Ending Balance: Collectively evaluated for impairment	316,923		336,781
Ending Balance: Loans acquired with deteriorated credit quality	503		525
Total loans	318,021		337,977
Ending Balance: Individually evaluated for impairment	4		5
Ending Balance: Collectively evaluated for impairment	2,307		2,405
Ending Balance	$ 2,311		$ 2,410