Loans and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 45,455	$ 24,322
Current	5,801,805	5,107,870
Total Loans	5,847,260	5,132,192
Recorded Investment  Greater than 89 Days and Still Accruing	165	0
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	33,117	14,480
Current	4,010,888	3,569,008
Total Loans	4,044,005	3,583,488
Recorded Investment  Greater than 89 Days and Still Accruing	0	0
Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,488
Current	744,690
Total Loans	751,178
Recorded Investment  Greater than 89 Days and Still Accruing	0
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,488
Current		429,502
Total Loans		430,990
Recorded Investment  Greater than 89 Days and Still Accruing		0
Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	689	530
Current	115,721	110,546
Total Loans	116,410	111,076
Recorded Investment  Greater than 89 Days and Still Accruing	0	0
Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,090	3,464
Current	340,074	331,337
Total Loans	342,164	334,801
Recorded Investment  Greater than 89 Days and Still Accruing	0	0
Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	694	967
Current	275,291	333,418
Total Loans	275,985	334,385
Recorded Investment  Greater than 89 Days and Still Accruing	0	0
Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,377	3,393
Current	315,141	334,059
Total Loans	317,518	337,452
Recorded Investment  Greater than 89 Days and Still Accruing	165	0
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,160	6,808
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,623	3,578
30-59 Days Past Due | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,892
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		353
30-59 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	246	166
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	429	1,138
30-59 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	970	1,573
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,055	1,889
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,071	1,200
60-89 Days Past Due | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	630
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		71
60-89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	80
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	167	251
60-89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	187	287
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27,240	15,625
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	22,423	9,702
Greater Than 89 Days Past Due | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	966
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,064
Greater Than 89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	443	284
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,494	2,075
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	694	967
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,220	$ 1,533