Loans, Leases and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 23,866	$ 36,136
Current	4,069,027	3,837,759
Total Loans and Leases	4,092,893	3,873,895
Recorded Investment Greater than 89 Days and Still Accruing	9	10
Commercial, Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,104	16,629
Current	2,768,795	2,539,972
Total Loans and Leases	2,776,899	2,556,601
Commercial, Industrial and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,276	1,448
Current	340,499	348,780
Total Loans and Leases	342,775	350,228
Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	713	363
Current	70,985	66,653
Total Loans and Leases	71,698	67,016
Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,740	9,377
Current	321,885	340,204
Total Loans and Leases	329,625	349,581
Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,237	4,881
Current	238,970	206,228
Total Loans and Leases	241,207	211,109
Home Equity and Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,796	3,438
Current	327,893	335,922
Total Loans and Leases	330,689	339,360
Recorded Investment Greater than 89 Days and Still Accruing	9	10
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,532	15,066
30-59 Days Past Due [Member] | Commercial, Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,616	6,082
30-59 Days Past Due [Member] | Commercial, Industrial and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,830	1,193
30-59 Days Past Due [Member] | Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	512	132
30-59 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,733	2,990
30-59 Days Past Due [Member] | Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		3,409
30-59 Days Past Due [Member] | Home Equity and Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	841	1,260
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,608	2,711
60-89 Days Past Due [Member] | Commercial, Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	678	1,234
60-89 Days Past Due [Member] | Commercial, Industrial and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	343	213
60-89 Days Past Due [Member] | Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	91	78
60-89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	320	1,057
60-89 Days Past Due [Member] | Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	765
60-89 Days Past Due [Member] | Home Equity and Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	411	129
Greater Than 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,726	18,359
Greater Than 89 Days Past Due [Member] | Commercial, Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,810	9,313
Greater Than 89 Days Past Due [Member] | Commercial, Industrial and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	103	42
Greater Than 89 Days Past Due [Member] | Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	110	153
Greater Than 89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,687	5,330
Greater Than 89 Days Past Due [Member] | Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,472	1,472
Greater Than 89 Days Past Due [Member] | Home Equity and Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,544	$ 2,049