Loans - Activity in Allowance for Loan Losses by Portfolio Segment (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
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 95,156	$ 93,589	$ 92,438	$ 104,453
Provision for loan losses	4,924	3,575	11,524	9,575
Charge-offs	(6,337)	(6,534)	(13,003)	(26,465)
Recoveries	4,543	2,770	7,327	5,837
Net charge-offs	(1,794)	(3,764)	(5,676)	(20,628)
Ending balance	98,286	93,400	98,286	93,400
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	57,054	51,085	52,790	54,164
Provision for loan losses	(248)	2,612	5,712	16,060
Charge-offs	(3,028)	(3,586)	(5,395)	(20,738)
Recoveries	1,894	703	2,565	1,328
Net charge-offs	(1,134)	(2,883)	(2,830)	(19,410)
Ending balance	55,672	50,814	55,672	50,814
Commercial Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21,020	24,809	22,590	29,346
Provision for loan losses	1,151	(1,108)	1,159	(5,974)
Charge-offs	(935)	(415)	(2,726)	(681)
Recoveries	810	287	1,023	882
Net charge-offs	(125)	(128)	(1,703)	201
Ending balance	22,046	23,573	22,046	23,573
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,533	5,148	5,230	5,252
Provision for loan losses	153	(246)	(567)	(74)
Charge-offs	(105)	(159)	(126)	(495)
Recoveries	78	174	122	234
Net charge-offs	(27)	15	(4)	(261)
Ending balance	4,659	4,917	4,659	4,917
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,691	3,724	5,010	3,507
Provision for loan losses	1,244	1,174	2,556	1,781
Charge-offs	(2,269)	(2,374)	(4,756)	(4,551)
Recoveries	1,761	1,606	3,617	3,393
Net charge-offs	(508)	(768)	(1,139)	(1,158)
Ending balance	6,427	4,130	6,427	4,130
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,858	8,823	6,818	12,184
Provision for loan losses	2,624	1,143	2,664	(2,218)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net charge-offs	0	0	0	0
Ending balance	$ 9,482	$ 9,966	$ 9,482	$ 9,966