Loans and the Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses (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
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			$ 52,699	$ 54,810
Allowance for loan commitments, beginning balance			341	468
Total beginning allowance for credit losses			53,040	55,278
Provision for loan losses			3,147	12,222
Provision for loan commitments			(24)	(117)
Total provision for credit losses	1,021	5,903	3,123	12,105
Charge-offs			(7,063)	(15,282)
Recoveries			1,598	1,860
Net charge-offs			(5,465)	(13,422)
Allowance for loan losses, ending balance	50,381	53,610	50,381	53,610
Allowance for loan commitments, ending balance	317	351	317	351
Total ending allowance for credit losses	50,698	53,961	50,698	53,961
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			3,741	4,842
Allowance for loan commitments, beginning balance			27	74
Total beginning allowance for credit losses			3,768	4,916
Provision for loan losses			559	2,969
Provision for loan commitments			11	(25)
Total provision for credit losses			570	2,944
Charge-offs			(373)	(3,377)
Recoveries			10	41
Net charge-offs			(363)	(3,336)
Allowance for loan losses, ending balance	3,937	4,475	3,937	4,475
Allowance for loan commitments, ending balance	38	49	38	49
Total ending allowance for credit losses	3,975	4,524	3,975	4,524
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			23,614	24,748
Allowance for loan commitments, beginning balance			25	21
Total beginning allowance for credit losses			23,639	24,769
Provision for loan losses			1,855	3,600
Provision for loan commitments			(2)	(11)
Total provision for credit losses			1,853	3,589
Charge-offs			(1,395)	(4,214)
Recoveries			420	587
Net charge-offs			(975)	(3,627)
Allowance for loan losses, ending balance	24,494	24,721	24,494	24,721
Allowance for loan commitments, ending balance	23	10	23	10
Total ending allowance for credit losses	24,517	24,731	24,517	24,731
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			9,326	11,414
Allowance for loan commitments, beginning balance			215	323
Total beginning allowance for credit losses			9,541	11,737
Provision for loan losses			(208)	740
Provision for loan commitments			(77)	(99)
Total provision for credit losses			(285)	641
Charge-offs			(919)	(2,342)
Recoveries			273	256
Net charge-offs			(646)	(2,086)
Allowance for loan losses, ending balance	8,472	10,068	8,472	10,068
Allowance for loan commitments, ending balance	138	224	138	224
Total ending allowance for credit losses	8,610	10,292	8,610	10,292
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			7,182	5,638
Allowance for loan commitments, beginning balance			6	4
Total beginning allowance for credit losses			7,188	5,642
Provision for loan losses			87	2,237
Provision for loan commitments				1
Total provision for credit losses			87	2,238
Charge-offs			(1,573)	(2,288)
Recoveries			113	193
Net charge-offs			(1,460)	(2,095)
Allowance for loan losses, ending balance	5,809	5,780	5,809	5,780
Allowance for loan commitments, ending balance	6	5	6	5
Total ending allowance for credit losses	5,815	5,785	5,815	5,785
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			2,458	1,962
Allowance for loan commitments, beginning balance			49	33
Total beginning allowance for credit losses			2,507	1,995
Provision for loan losses			(32)	1,125
Provision for loan commitments			44	15
Total provision for credit losses			12	1,140
Charge-offs			(346)	(655)
Recoveries			43	9
Net charge-offs			(303)	(646)
Allowance for loan losses, ending balance	2,123	2,441	2,123	2,441
Allowance for loan commitments, ending balance	93	48	93	48
Total ending allowance for credit losses	2,216	2,489	2,216	2,489
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			5,557	5,410
Allowance for loan commitments, beginning balance			19	13
Total beginning allowance for credit losses			5,576	5,423
Provision for loan losses			836	1,413
Provision for loan commitments				2
Total provision for credit losses			836	1,415
Charge-offs			(2,043)	(2,017)
Recoveries			607	613
Net charge-offs			(1,436)	(1,404)
Allowance for loan losses, ending balance	4,957	5,419	4,957	5,419
Allowance for loan commitments, ending balance	19	15	19	15
Total ending allowance for credit losses	4,976	5,434	4,976	5,434
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			821	796
Allowance for loan commitments, beginning balance
Total beginning allowance for credit losses			821	796
Provision for loan losses			50	138
Provision for loan commitments
Total provision for credit losses			50	138
Charge-offs			(414)	(389)
Recoveries			132	161
Net charge-offs			(282)	(228)
Allowance for loan losses, ending balance	589	706	589	706
Allowance for loan commitments, ending balance
Total ending allowance for credit losses	$ 589	$ 706	$ 589	$ 706