Loans and the Allowance for Credit Losses - Summary of Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	$ 69,202		$ 69,202		$ 73,404
Recorded Investment	62,338		62,338		63,653
Related Allowance	3,443		3,443		1,743
Average Recorded Investment	62,743	74,547	63,046	78,665
Interest Income Recognized	484	415	972	830
Impaired loans with no related specific allowance recorded [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	62,822		62,822		67,679
Recorded Investment	55,958		55,958		58,044
Related Allowance
Average Recorded Investment	57,035	62,411	57,371	66,940
Interest Income Recognized	458	344	918	650
Impaired loans with no related specific allowance recorded [Member] | Commercial Real Estate - Land and Construction [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	7,025		7,025		9,278
Recorded Investment	5,150		5,150		5,577
Related Allowance
Average Recorded Investment	5,704	9,249	5,661	11,076
Interest Income Recognized	37	80	97	172
Impaired loans with no related specific allowance recorded [Member] | Commercial Real Estate - Improved Property [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	26,882		26,882		27,515
Recorded Investment	24,981		24,981		24,455
Related Allowance
Average Recorded Investment	24,428	30,151	24,437	31,551
Interest Income Recognized	185	162	316	282
Impaired loans with no related specific allowance recorded [Member] | Commercial and Industrial [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	4,465		4,465		4,546
Recorded Investment	3,716		3,716		4,019
Related Allowance
Average Recorded Investment	3,974	6,860	3,989	7,599
Interest Income Recognized	28	41	61	59
Impaired loans with no related specific allowance recorded [Member] | Residential Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	20,431		20,431		22,146
Recorded Investment	18,679		18,679		20,269
Related Allowance
Average Recorded Investment	19,462	14,946	19,731	15,371
Interest Income Recognized	171	60	365	134
Impaired loans with no related specific allowance recorded [Member] | Home Equity [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	2,320		2,320		2,437
Recorded Investment	2,028		2,028		2,207
Related Allowance
Average Recorded Investment	2,034	988	2,092	1,102
Interest Income Recognized	15		30	2
Impaired loans with no related specific allowance recorded [Member] | Consumer [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	1,699		1,699		1,757
Recorded Investment	1,404		1,404		1,517
Related Allowance
Average Recorded Investment	1,433	217	1,461	241
Interest Income Recognized	22	1	49	1
Impaired loans with a specific allowance recorded [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	6,380		6,380		5,725
Recorded Investment	6,380		6,380		5,609
Related Allowance	3,443		3,443		1,743
Average Recorded Investment	5,708	12,136	5,675	11,725
Interest Income Recognized	26	71	54	180
Impaired loans with a specific allowance recorded [Member] | Commercial Real Estate - Land and Construction [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	1,536		1,536		1,627
Recorded Investment	1,536		1,536		1,627
Related Allowance	839		839		832
Average Recorded Investment	1,540	4,188	1,569	3,730
Interest Income Recognized	9		22
Impaired loans with a specific allowance recorded [Member] | Commercial Real Estate - Improved Property [Member]
Schedule Of Financial Receivables [Line Items]
Unpaid Principal Balance	4,844		4,844		4,098
Recorded Investment	4,844		4,844		3,982
Related Allowance	2,604		2,604		911
Average Recorded Investment	4,168	7,948	4,106	7,995
Interest Income Recognized	$ 17	$ 71	$ 32	$ 180