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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 98,286	$ 93,400	$ 92,438	$ 104,453
Provision for loan losses	390	5,108	11,914	14,683
Charge-offs	(7,261)	(8,142)	(20,264)	(34,607)
Recoveries	6,897	2,781	14,224	8,618
Net charge-offs	(364)	(5,361)	(6,040)	(25,989)
Ending balance	98,312	93,147	98,312	93,147
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	55,672	50,814	52,790	54,164
Provision for loan losses	2,224	8,060	7,936	24,120
Charge-offs	(3,631)	(4,962)	(9,026)	(25,700)
Recoveries	4,371	666	6,936	1,994
Net charge-offs	740	(4,296)	(2,090)	(23,706)
Ending balance	58,636	54,578	58,636	54,578
Commercial Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	22,046	23,573	22,590	29,346
Provision for loan losses	4,650	(1,983)	5,809	(7,957)
Charge-offs	(393)	(56)	(3,119)	(737)
Recoveries	477	182	1,500	1,064
Net charge-offs	84	126	(1,619)	327
Ending balance	26,780	21,716	26,780	21,716
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,659	4,917	5,230	5,252
Provision for loan losses	1,057	638	490	564
Charge-offs	(714)	(514)	(840)	(1,009)
Recoveries	105	57	227	291
Net charge-offs	(609)	(457)	(613)	(718)
Ending balance	5,107	5,098	5,107	5,098
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,427	4,130	5,010	3,507
Provision for loan losses	1,941	1,286	4,497	3,067
Charge-offs	(2,523)	(2,610)	(7,279)	(7,161)
Recoveries	1,944	1,876	5,561	5,269
Net charge-offs	(579)	(734)	(1,718)	(1,892)
Ending balance	7,789	4,682	7,789	4,682
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	9,482	9,966	6,818	12,184
Provision for loan losses	(9,482)	(2,893)	(6,818)	(5,111)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net charge-offs	0	0	0	0
Ending balance	$ 0	$ 7,073	$ 0	$ 7,073