Loans and Leases and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 12,179	$ 19,008
Current	4,448,268	4,137,672
Total Loans and Leases	4,460,447	4,156,680
Recorded Investment Greater than 89 Days and Still Accruing	0	200
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,353	8,562
Current	3,053,426	2,822,622
Total Loans and Leases	3,057,779	2,831,184
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	1,166	257
Current	335,569	340,143
Total Loans and Leases	336,735	340,400
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,047	779
Current	86,878	74,260
Total Loans and Leases	87,925	75,039
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	2,630	4,984
Current	327,224	317,896
Total Loans and Leases	329,854	322,880
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	0	1,472
Current	319,545	263,436
Total Loans and Leases	319,545	264,908
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	2,983	2,954
Current	325,626	319,315
Total Loans and Leases	328,609	322,269
Recorded Investment Greater than 89 Days and Still Accruing	0	200
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,843	6,436
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,477	3,663
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	173	80
30-59 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	533	496
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	743	939
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	1,917	1,258
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,222	2,560
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	639	1,082
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	243	121
60-89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13	139
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	111	908
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	216	310
Greater Than 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,114	10,012
Greater Than 89 Days | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,237	3,817
Greater Than 89 Days | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	750	56
Greater Than 89 Days | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	501	144
Greater Than 89 Days | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,776	3,137
Greater Than 89 Days | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	1,472
Greater Than 89 Days | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 850	$ 1,386