Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 93,400	$ 105,648	$ 104,453	$ 110,147
Provision for loan losses	5,108	2,500	14,683	5,955
Charge-offs	(8,142)	(8,957)	(34,607)	(24,747)
Recoveries	2,781	6,210	8,618	14,046
Net charge-offs	(5,361)	(2,747)	(25,989)	(10,701)
Ending balance	93,147	105,401	93,147	105,401
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	50,814	53,475	54,164	42,774
Provision for loan losses	8,060	2,723	24,120	18,275
Charge-offs	(4,962)	(5,837)	(25,700)	(13,323)
Recoveries	666	1,181	1,994	3,816
Net charge-offs	(4,296)	(4,656)	(23,706)	(9,507)
Ending balance	54,578	51,542	54,578	51,542
Commercial Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	23,573	27,631	29,346	20,912
Provision for loan losses	(1,983)	(2,682)	(7,957)	5,882
Charge-offs	(56)	(520)	(737)	(3,715)
Recoveries	182	3,212	1,064	4,562
Net charge-offs	126	2,692	327	847
Ending balance	21,716	27,641	21,716	27,641
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,917	5,235	5,252	3,540
Provision for loan losses	638	315	564	2,295
Charge-offs	(514)	(209)	(1,009)	(1,104)
Recoveries	57	53	291	663
Net charge-offs	(457)	(156)	(718)	(441)
Ending balance	5,098	5,394	5,098	5,394
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,130	3,649	3,507	12,635
Provision for loan losses	1,286	880	3,067	(7,133)
Charge-offs	(2,610)	(2,391)	(7,161)	(6,605)
Recoveries	1,876	1,764	5,269	5,005
Net charge-offs	(734)	(627)	(1,892)	(1,600)
Ending balance	4,682	3,902	4,682	3,902
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	9,966	15,658	12,184	30,286
Provision for loan losses	(2,893)	1,264	(5,111)	(13,364)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net charge-offs	0	0	0	0
Ending balance	$ 7,073	$ 16,922	$ 7,073	$ 16,922