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	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	100.00%	100.00%
Total Commercial Loans	$ 2,518,034	$ 2,428,509
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	26,772	19,631
Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	124,997	113,732
Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	12,417	11,489
Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	10,103	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	174,289	153,382
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	93.00%	94.00%
Total Commercial Loans	2,343,745	2,275,127
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	857,354	810,882
Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	10,037	12,566
Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	63,462	56,806
Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,592	2,362
Commercial [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,517	2,641
Commercial [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	77,608	74,375
Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	779,746	736,507
Owner-Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	778,257	786,360
Owner-Occupied Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	7,186	4,747
Owner-Occupied Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	45,524	45,181
Owner-Occupied Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,615	5,185
Owner-Occupied Commercial [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,313	12
Owner-Occupied Commercial [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	57,638	55,125
Owner-Occupied Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	720,619	731,235
Commercial Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	763,090	725,193
Commercial Mortgage [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	9,249	2,092
Commercial Mortgage [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	13,881	8,146
Commercial Mortgage [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	8,210	2,784
Commercial Mortgage [Member] | Doubtful / Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	5,273	5,877
Commercial Mortgage [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	36,613	18,899
Commercial Mortgage [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	726,477	706,294
Construction Loan Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	119,333	106,074
Construction Loan Commitments [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	300	226
Construction Loan Commitments [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,130	3,599
Construction Loan Commitments [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans		1,158
Construction Loan Commitments [Member] | Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,430	4,983
Construction Loan Commitments [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	$ 116,903	$ 101,091