Loans and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 45,201	$ 24,322
Current	5,278,628	5,107,870
Total Loans	5,323,829	5,132,192
Recorded Investment Greater than 89 Days and Still Accruing	99	0
Commercial, secured by real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	33,384	14,480
Current	3,701,509	3,569,008
Total Loans	3,734,893	3,583,488
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Total Past Due	4,168	1,488
Current	462,284	429,502
Total Loans	466,452	430,990
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Equipment finance
Financing Receivable, Past Due [Line Items]
Total Past Due	494	530
Current	115,927	110,546
Total Loans	116,421	111,076
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Total Past Due	3,743	3,464
Current	329,970	331,337
Total Loans	333,713	334,801
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Real estate - construction
Financing Receivable, Past Due [Line Items]
Total Past Due	225	967
Current	332,570	333,418
Total Loans	332,795	334,385
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Home equity and consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	3,187	3,393
Current	336,368	334,059
Total Loans	339,555	337,452
Recorded Investment Greater than 89 Days and Still Accruing	99	0
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	18,160	6,808
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	12,162	3,578
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Total Past Due	2,101	353
30-59 Days Past Due | Equipment finance
Financing Receivable, Past Due [Line Items]
Total Past Due	264	166
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Total Past Due	1,988	1,138
30-59 Days Past Due | Real estate - construction
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Home equity and consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	1,645	1,573
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	9,496	1,889
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	8,032	1,200
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Total Past Due	1,010	71
60-89 Days Past Due | Equipment finance
Financing Receivable, Past Due [Line Items]
Total Past Due	30	80
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Total Past Due	125	251
60-89 Days Past Due | Real estate - construction
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Home equity and consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	299	287
Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	17,545	15,625
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	13,190	9,702
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Total Past Due	1,057	1,064
Greater Than 89 Days Past Due | Equipment finance
Financing Receivable, Past Due [Line Items]
Total Past Due	200	284
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Total Past Due	1,630	2,075
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Past Due [Line Items]
Total Past Due	225	967
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 1,243	$ 1,533