Loans and the Allowance for Credit Losses - Recorded Investment in Non-Accrual Loans and TDRs (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Non-accrual loans	$ 36,118	$ 36,633
TDRs	19,794	24,185
Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	13,513	14,861
Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	6,281	9,324
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	1,950	2,564
TDRs	1,008	1,601
Commercial Real Estate - Land and Construction [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,008	1,601
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	15,946	17,305
TDRs	5,178	6,710
Commercial Real Estate - Improved Property [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	3,234	3,052
Commercial Real Estate - Improved Property [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	1,944	3,658
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	17,896	19,869
TDRs	6,186	8,311
Commercial Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	3,234	3,052
Commercial Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	2,952	5,259
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	6,167	4,380
TDRs	625	994
Commercial and Industrial [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	222	415
Commercial and Industrial [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	403	579
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	10,137	10,240
TDRs	11,168	12,841
Residential Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	8,754	9,850
Residential Real Estate [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	2,414	2,991
Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	1,283	1,604
TDRs	1,052	1,191
Home Equity [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	835	902
Home Equity [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	217	289
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Non-accrual loans	635	540
TDRs	763	848
Consumer [Member] | Accruing TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	468	642
Consumer [Member] | Non-Accrual TDRs [Member]
Financing Receivable, Impaired [Line Items]
TDRs	$ 295	$ 206