Loans and the Allowance for Credit Losses - Recorded Investment in Non-Accrual Loans and TDRs (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	$ 43,069	$ 39,372
TDRs	34,924	39,282
Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	19,269	24,281
Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	15,655	15,001
Commercial Real Estate - Land and Construction [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	5,716	4,668
TDRs	4,909	5,472
Commercial Real Estate - Land and Construction [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	969	2,537
Commercial Real Estate - Land and Construction [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	3,940	2,935
Commercial Real Estate - Improved Property [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	24,409	18,239
TDRs	12,927	16,650
Commercial Real Estate - Improved Property [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	5,417	10,198
Commercial Real Estate - Improved Property [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	7,510	6,452
Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	30,125	22,907
TDRs	17,836	22,122
Commercial Real Estate [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	6,386	12,735
Commercial Real Estate [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	11,450	9,387
Commercial and Industrial [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	3,148	3,387
TDRs	1,119	1,360
Commercial and Industrial [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	568	632
Commercial and Industrial [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	551	728
Residential Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	8,130	11,247
TDRs	13,473	13,099
Residential Real Estate [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	10,549	9,022
Residential Real Estate [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	2,924	4,077
Home Equity [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	1,024	1,184
TDRs	1,344	1,541
Home Equity [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	1,004	1,022
Home Equity [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	340	519
Consumer [Member]
Schedule Of Financial Receivables [Line Items]
Non-accrual loans	642	647
TDRs	1,152	1,160
Consumer [Member] | Accruing TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	762	870
Consumer [Member] | Non Accrual TDRs [Member]
Schedule Of Financial Receivables [Line Items]
TDRs	$ 390	$ 290