Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 133,802		$ 124,704
Loans charged-off	(36,648)	[1]	(48,715)	[1]
Charged-off loans recovered	7,406		5,061
Net charge-offs	(29,242)		(43,654)
Provision for loan losses	25,640		52,752	[2]
Ending balance	130,200		133,802
Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	73,649		61,967
Loans charged-off	(16,103)	[1]	(29,229)	[1]
Charged-off loans recovered	4,475		2,365
Net charge-offs	(11,628)		(26,864)
Provision for loan losses	2,349		38,546	[2]
Ending balance	64,370		73,649
Commercial real estate loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	34,637		30,409
Loans charged-off	(11,688)	[1]	(10,358)	[1]
Charged-off loans recovered	272		331
Net charge-offs	(11,416)		(10,027)
Provision for loan losses	20,848		14,255	[2]
Ending balance	44,069		34,637
Residential mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	9,120		9,476
Loans charged-off	(3,518)	[1]	(3,222)	[1]
Charged-off loans recovered	701		129
Net charge-offs	(2,817)		(3,093)
Provision for loan losses	3,120		2,737	[2]
Ending balance	9,423		9,120
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,677		14,499
Loans charged-off	(5,339)	[1]	(5,906)	[1]
Charged-off loans recovered	1,958		2,236
Net charge-offs	(3,381)		(3,670)
Provision for loan losses	246		(2,152)	[2]
Ending balance	5,542		8,677
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,719		8,353
Loans charged-off		[1]
Charged-off loans recovered
Net charge-offs
Provision for loan losses	(923)		(634)	[2]
Ending balance	$ 6,796		$ 7,719

[1] The allowance for covered loans was reduced by loan charge-offs totaling $4.0 million and $14.4 million during 2012 and 2011, respectively, primarily in the commercial and industrial loan portfolio.

[2] The provision for covered loan losses totaled $21.5 million for the year ended December 31, 2011.