Loans, Leases and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 23,025	$ 19,008
Current	4,205,027	4,137,672
Total Loans and Leases	4,228,052	4,156,680
Recorded Investment Greater than 89 Days and Still Accruing	1	200
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,850	8,562
Current	2,876,147	2,822,622
Total Loans and Leases	2,885,997	2,831,184
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	882	257
Current	338,783	340,143
Total Loans and Leases	339,665	340,400
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,225	779
Current	77,013	74,260
Total Loans and Leases	78,238	75,039
Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,574	4,984
Current	317,480	317,896
Total Loans and Leases	323,054	322,880
Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,472	1,472
Current	281,906	263,436
Total Loans and Leases	283,378	264,908
Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,022	2,954
Current	313,698	319,315
Total Loans and Leases	317,720	322,269
Recorded Investment Greater than 89 Days and Still Accruing	1	200
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,988	6,436
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,619	3,663
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	650	80
30-59 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	167	496
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,221	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	2,331	1,258
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,263	2,560
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	57	1,082
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	121
60-89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	808	139
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	162	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	236	310
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,774	10,012
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,174	3,817
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	232	56
Greater Than 89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	250	144
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,191	3,137
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,472	1,472
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,455	$ 1,386