Allowance for Loan Losses and Credit Quality Information - Analysis of Problem Loans, by Credit Risk Profile Using Internally Assigned Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	100.00%	100.00%
Total Commercial Loans	$ 2,485,208	$ 2,428,509
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	19,424	19,631
Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	119,734	113,732
Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	18,494	11,489
Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	9,263	8,530
Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	7.00%	6.00%
Total Commercial Loans	166,915	153,382
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	93.00%	94.00%
Total Commercial Loans	2,318,293	2,275,127
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	838,181	810,882
Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	14,696	12,566
Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	58,610	56,806
Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,347	2,362
Commercial [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,236	2,641
Commercial [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	77,889	74,375
Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	760,292	736,507
Owner-Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	799,213	786,360
Owner-Occupied Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	3,967	4,747
Owner-Occupied Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	44,357	45,181
Owner-Occupied Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	4,564	5,185
Owner-Occupied Commercial [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,754	12
Owner-Occupied Commercial [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	54,642	55,125
Owner-Occupied Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	744,571	731,235
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	746,329	725,193
Commercial Mortgages [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	501	2,092
Commercial Mortgages [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	13,180	8,146
Commercial Mortgages [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	10,513	2,784
Commercial Mortgages [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	5,273	5,877
Commercial Mortgages [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	29,467	18,899
Commercial Mortgages [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	716,862	706,294
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	101,485	106,074
Construction [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	260	226
Construction [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	3,587	3,599
Construction [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,070	1,158
Construction [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans
Construction [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	4,917	4,983
Construction [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	$ 96,568	$ 101,091