Loans - Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 4,808,672	$ 4,828,612	$ 4,486,301
Commercial mortgages	2,746,821	2,495,481
Construction	412,529	608,306
Land	211,619	216,008
Total commercial real estate	3,370,969	3,319,795	3,250,135
Home equity loans	331,349	310,675
Home equity lines of credit	193,449	186,522
1-4 family residential mortgages	33,568	38,323
Construction	9,884	17,621
Other	231,577	224,206
Total consumer real estate	799,827	777,347	768,482
Total real estate	4,170,796	4,097,142
Consumer installment	333,885	311,310
Other	16,227	8,435
Total consumer and other	350,112	319,745	325,592
Unearned discounts	(23,126)	(21,651)	(19,470)
Total loans	9,306,454	9,223,848	8,811,040
Total commercial and industrial percentage of total loans	51.70%	52.30%
Commercial mortgages percentage of total loans	29.50%	27.10%
Construction percentage of total loans	4.40%	6.60%
Land percentage of total loans	2.30%	2.30%
Total commercial real estate percentage of total loans	36.20%	36.00%
Home equity loans percentage of total loans	3.50%	3.40%
Home equity lines of credit percentage of total loans	2.10%	2.00%
1-4 family residential mortgages percentage of total loans	0.30%	0.40%
Construction percentage of total loans	0.10%	0.20%
Other percentage of total loans	2.50%	2.40%
Total consumer real estate percentage of total loans	8.50%	8.40%
Total real estate percentage of total loans	44.70%	44.40%
Consumer installment percentage of total loans	3.60%	3.40%
Other percentage of total loans	0.20%	0.10%
Total consumer and other percentage of total loans	3.80%	3.50%
Unearned discounts percentage of total loans	(0.20%)	(0.20%)
Total loans percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	4,357,696	4,357,100
Total commercial and industrial percentage of total loans	46.80%	47.20%
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	306,649	278,535
Total commercial and industrial percentage of total loans	3.30%	3.00%
Asset-based [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 144,327	$ 192,977
Total commercial and industrial percentage of total loans	1.60%	2.10%