Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	$ 3,706,327	$ 3,533,741
Loans, 30 to 59 Days Past Due	4,164	8,535
Loans, 60 to 89 Days Past Due	2,751	3,605
Total nonaccrual loans	14,939	22,454
Loans, Past Due, Total	21,854	34,594
Total Loans	3,728,181	3,568,335
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	1,629,928	1,595,590
Loans, 30 to 59 Days Past Due	753	1,209
Loans, 60 to 89 Days Past Due	44	207
Total nonaccrual loans	5,658	10,750
Loans, Past Due, Total	6,455	12,166
Total Loans	1,636,383	1,607,756
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	918,846	836,276
Loans, 30 to 59 Days Past Due	559	2,599
Loans, 60 to 89 Days Past Due	249	278
Total nonaccrual loans	2,537	3,296
Loans, Past Due, Total	3,345	6,173
Total Loans	922,191	842,449
Commercial Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	185,428	139,133
Loans, 30 to 59 Days Past Due	0	1,049
Loans, 60 to 89 Days Past Due	1,014	751
Total nonaccrual loans	1,869	2,742
Loans, Past Due, Total	2,883	4,542
Total Loans	188,311	143,675
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	488,551	481,260
Loans, 30 to 59 Days Past Due	1,022	828
Loans, 60 to 89 Days Past Due	898	1,666
Total nonaccrual loans	2,118	3,338
Loans, Past Due, Total	4,038	5,832
Total Loans	492,589	487,092
Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	412,851	408,777
Loans, 30 to 59 Days Past Due	1,466	2,468
Loans, 60 to 89 Days Past Due	478	659
Total nonaccrual loans	1,431	2,291
Loans, Past Due, Total	3,375	5,418
Total Loans	416,226	414,195
Installment and Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	65,380	67,420
Loans, 30 to 59 Days Past Due	364	382
Loans, 60 to 89 Days Past Due	68	44
Total nonaccrual loans	26	37
Loans, Past Due, Total	458	463
Total Loans	65,838	67,883
Consumer Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	3,541	3,149
Loans, 30 to 59 Days Past Due	0	0
Loans, 60 to 89 Days Past Due	0	0
Total nonaccrual loans	0	0
Loans, Past Due, Total	0	0
Total Loans	3,541	3,149
Loans Held for Sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	1,802	2,136
Loans, 30 to 59 Days Past Due	0	0
Loans, 60 to 89 Days Past Due	0	0
Total nonaccrual loans	1,300	0
Loans, Past Due, Total	1,300	0
Total Loans	$ 3,102	$ 2,136