Loans and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 27,123	$ 12,022
Current	4,884,127	4,447,773
Total Loans	4,911,250	4,459,795
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,555	4,196
Current	3,408,255	3,052,931
Total Loans	3,424,810	3,057,127
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,606	1,166
Current	403,654	335,569
Total Loans	405,260	336,735
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	452	1,047
Current	98,899	86,878
Total Loans	99,351	87,925
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	4,523	2,630
Current	331,825	327,224
Total Loans	336,348	329,854
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	493	0
Current	301,607	319,545
Total Loans	302,100	319,545
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	3,494	2,983
Current	339,887	325,626
Total Loans	343,381	328,609
Recorded Investment Greater than 89 Days and Still Accruing	0	0
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,086	4,843
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,398	1,477
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,321	173
30-59 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	248	533
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,038	743
30-59 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	493	0
30-59 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,588	1,917
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,609	1,222
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,947	639
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	154	243
60-89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	68	13
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	223	111
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	217	216
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,428	5,957
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,210	2,080
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	131	750
Greater Than 89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	136	501
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,262	1,776
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,689	$ 850