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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 53,823		$ 53,823		$ 56,215
Recorded Investment	49,631		49,631		51,494
Related Allowance	1,068		1,068		732
Average Recorded Investment	50,273	62,743	50,677	63,046
Interest Income Recognized	478	484	774	972
Impaired Loans with No Related Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	51,137		51,137		53,940
Recorded Investment	46,945		46,945		49,219
Average Recorded Investment	47,009	57,035	47,744	57,371
Interest Income Recognized	446	458	729	918
Impaired Loans with No Related Specific Allowance Recorded [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,050		2,050		2,663
Recorded Investment	1,950		1,950		2,564
Average Recorded Investment	2,143	5,704	2,283	5,661
Interest Income Recognized	13	37	15	97
Impaired Loans with No Related Specific Allowance Recorded [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	19,719		19,719		21,421
Recorded Investment	18,455		18,455		19,628
Average Recorded Investment	18,572	24,428	18,924	24,437
Interest Income Recognized	133	185	153	316
Impaired Loans with No Related Specific Allowance Recorded [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	4,970		4,970		3,773
Recorded Investment	4,428		4,428		3,249
Average Recorded Investment	4,122	3,974	3,831	3,989
Interest Income Recognized	57	28	89	61
Impaired Loans with No Related Specific Allowance Recorded [Member] | Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	20,726		20,726		22,006
Recorded Investment	18,891		18,891		20,090
Average Recorded Investment	18,864	19,462	19,272	19,731
Interest Income Recognized	209	171	391	365
Impaired Loans with No Related Specific Allowance Recorded [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,355		2,355		2,675
Recorded Investment	2,118		2,118		2,506
Average Recorded Investment	2,173	2,034	2,284	2,092
Interest Income Recognized	16	15	35	30
Impaired Loans with No Related Specific Allowance Recorded [Member] | Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	1,317		1,317		1,402
Recorded Investment	1,103		1,103		1,182
Average Recorded Investment	1,135	1,433	1,150	1,461
Interest Income Recognized	18	22	46	49
Impaired Loans with a Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,686		2,686		2,275
Recorded Investment	2,686		2,686		2,275
Related Allowance	1,068		1,068		732
Average Recorded Investment	3,264	5,708	2,933	5,675
Interest Income Recognized	32	26	45	54
Impaired Loans with a Specific Allowance Recorded [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		1,540		1,569
Interest Income Recognized		9		22
Impaired Loans with a Specific Allowance Recorded [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	725		725		729
Recorded Investment	725		725		729
Related Allowance	39		39		51
Average Recorded Investment	727	4,168	727	4,106
Interest Income Recognized	3	17	4	32
Impaired Loans with a Specific Allowance Recorded [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	1,961		1,961		1,546
Recorded Investment	1,961		1,961		1,546
Related Allowance	1,029		1,029		681
Average Recorded Investment	2,537		2,206
Interest Income Recognized	$ 29		$ 41