Loans, Leases and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 19,942	$ 19,008
Current	4,312,296	4,137,672
Total Loans and Leases	4,332,238	4,156,680
Recorded Investment Greater than 89 Days and Still Accruing	16	200
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,789	8,562
Current	2,975,641	2,822,622
Total Loans and Leases	2,984,430	2,831,184
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	897	257
Current	333,344	340,143
Total Loans and Leases	334,241	340,400
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,006	779
Current	81,875	74,260
Total Loans and Leases	82,881	75,039
Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,502	4,984
Current	310,633	317,896
Total Loans and Leases	315,135	322,880
Recorded Investment Greater than 89 Days and Still Accruing	16
Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,071	1,472
Current	296,445	263,436
Total Loans and Leases	297,516	264,908
Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,677	2,954
Current	314,358	319,315
Total Loans and Leases	318,035	322,269
Recorded Investment Greater than 89 Days and Still Accruing		200
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,654	6,436
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,068	3,663
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	540	80
30-59 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	454	496
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,470	939
30-59 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,071	0
30-59 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,051	1,258
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,333	2,560
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,393	1,082
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7	121
60-89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	110	139
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	207	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	616	310
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,955	10,012
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,328	3,817
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	350	56
Greater Than 89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	442	144
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,825	3,137
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	1,472
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,010	$ 1,386